Asus ZenFone 2 Review

Asus’ 5.5-inch smartphone comes with an Intel processor and 4GB of RAM. Will its PC-like approach to creating smartphones leave you in a Zen-like state?

Early Verdict

Its camera may be average, but its audio quality and system performance rival those of flagship devices for only a fraction of the cost. The 1080p 5.5-inch IPS display is incredibly sharp and it comes with 4GB of RAM; features you do not usually find at this price. True to its PC heritage, Asus provides power users plenty of options for customizing the OS.


  • +

    Price • Performance • Audio quality • ZenUI, microSD support • Dual Active SIM


  • -

    Ergonomics • Display brightness

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Asus has long been a powerhouse in the computer industry. The company produces peripherals and components such as monitors, sound cards, and graphics cards. Asus also makes complete systems, including the Republic of Gamers desktops and laptops, ultrabooks, and all-in-one PCs. Asus even introduced what many saw as the first real contender to the iPad: the Eee Pad Transformer. With a higher screen resolution, full keyboard, and full-size USB ports, the Eee Pad Transformer promised laptop functionality in a tablet convertible form factor. The company then went on to produce one of the most well loved tablets on the market at the time — Google’s Nexus 7.

Despite not being well known as a smartphone manufacturer, Asus has had a long history in the smartphone field. Starting in 2006, the company released various phones and pocket PCs running Microsoft’s Windows Mobile OS. In 2012 the company released the Padfone, its first Android phone. Before phablets became all the rage, Asus came up with a phone and tablet dock combination that allowed the phone to be inserted into the the back of the tablet to provide a larger screen. Asus also released the Fonepad, essentially a 7-inch tablet with a cellular data connection. Then in 2014, the company released the first generation ZenFone with three different models. The ZenFone 4, ZenFone 5, and Zenfone 6, with screen sizes corresponding to the product names, had screen densities below 300 PPI and two variations of a dual-core Intel Atom processor, placing these devices in the mid-range market.

Despite its various offerings, Asus has had difficulty breaking into the US smartphone market. The company managed to get its Padfone X and Padfone X mini picked up by AT&T but neither really became blockbusters. Instead of going the carrier route, Asus has focused on selling its devices at full price online and in electronics stores. This method works well overseas, however, the average US consumer is used to purchasing a phone from a carrier and signing a two year contract to subsidize the cost. But in recent years, carriers have started moving toward device payment plans, where the full price of the device is simply split up over a set period of time and tacked on to the monthly bill. And with a growing number of phones in the $200 to $300 price range, many customers have begun to realize that paying full price for a smartphone may not be such a bad idea if it saves them money in the long run and lets them upgrade faster.

This shift in the market could be advantageous for Asus’ latest smartphone, the ZenFone 2, whose 5.5-inch HD screen, quad-core Atom CPU, and a generous 4GB of RAM—the same amount of RAM found in most Chromebooks—make it a compelling mid-range option.

Technical Specifications

We're used to seeing smartphone CPUs based on the ARMv7 or ARMv8 RISC (reduced instruction set computing) architecture from companies such as Apple, MediaTek, Qualcomm, and Samsung, but the ZenFone 2 is different. It's powered by Intel's x86 CISC (complex instruction set computing) architecture, originally designed for PC applications with relatively large power envelopes. Instead of scaling down a power-hungry PC CPU like Intel, ARM took the opposite approach, optimizing its architecture for low-power applications from the beginning, an approach that has given ARM a near monopoly on smartphone CPUs. However, Intel has continued to improve its Atom CPU to where it should now provide similar performance and stamina to the ARM-based offerings.

There are two versions of the ZenFone 2 for North America, both sporting Intel Atom 64-bit processors. It will be interesting to see how the Atom CPU compares to its ARM-based competition in our performance and battery life tests. Graphics for both versions are provided by the PowerVR G6430 GPU. This is the same unit found in the iPhone 5s, which still offers good performance.

Asus manages to keep the overall size relatively manageable, packing everything into an elegant, curved-back case just slightly bigger than the LG G4 but smaller than the Galaxy Note 4. The weight, at 170 grams, is slightly lighter than the iPhone 6 Plus but heavier than the OnePlus One.

The ZenFone 2 features a 3000mAh non-removable battery, slightly larger than the iPhone 6 Plus’ battery and the same size as the LG G4. It also comes with Asus BoostMaster technology which provides a 60% charge in 39 minutes according to Asus.

The ZenFone 2’s rear camera uses a 13 MP Toshiba sensor paired with an f/2.0 aperture lens. The Nexus 6, Moto G (3rd gen), and OnePlus 2 all use 13 MP Sony sensors with f/2.0 aperture lenses too, so the ZenFone 2 looks competitive, at least on paper. The front camera is a 5 MP wide-angle affair for higher resolution selfies.


There are two different model numbers for the ZenFone 2, each with several different SKUs. The ZE550ML will be sold in markets outside of the US, while the ZE551ML is the US model we are reviewing. It’s available with 16, 32, or 64GB of internal storage, with an additional 64GB available when using a microSD card. The 16GB SKU comes with a 1.8GHz Atom Z3560 SoC and 2GB RAM, while the 32GB and 64GB versions are equipped with the 2.3GHz Atom Z3580 SoC and 4GB RAM. The 18W BoostMaster adapter, necessary to enable the quick charging feature, only comes with the 2.3GHz versions. Color choices include Glacier Gray, Glamour Red, Ceramic White, Osmium Black, and Sheer Gold.

Being the first smartphone to ship with 4GB of RAM is impressive, but perhaps the ZenFone 2’s most disruptive feature is the price. At $200 for the 16GB version and $300 for the 64GB version, it’s almost a steal. These are prices one would expect to pay for the newest flagship phone on a two year contract. For comparison, a 64GB iPhone 6 Plus costs $849 and a 64GB Galaxy S6 starts at $700. It can be purchased online from several retailers, including Newegg, Groupon, Amazon, and B&H in the US, and Newegg, Canada Computers, Memory Express, and NCIX in Canada.


Swipe to scroll horizontally
Model NumberZE550MLZE551ML
CarriersAT&T, T-Mobile
BasebandIntel X-GOLD 726
RF TransceiverIntel SMARTi 4.5
RF ICsSkyworks SKY77597 antenna switch
LTEWorld: 1/2/3/4/5/7/8/20Taiwan: 1/2/3/4/5/8/28China/India: 1/3 (FDD-LTE)China/India: 38/39/40/41 (TDD-LTE)US: 1/2/3/4/5/7/8/17/20World: 1/2/3/4/5/7/8/20Taiwan: 1/2/3/4/5/8/9/18/19/28China/India: 1/3 (FDD-LTE)China/India: 38/39/40/41 (TDD-LTE)
GSMWorld: 850/900/1800/1900 MHzWorld: 850/900/1800/1900 MHz
WCDMAWorld: 1/2/5/8World: 1/2/5/8China/India: 1/2 (TD-SCDMA)

There are a total of five different SKUs of the ZenFone 2, four supporting various FDD-LTE frequency bands and one for the Chinese and Indian markets. The US SKU of model ZE551ML supports the AT&T and T-Mobile networks, along with their respective MVNOs.

The ZenFone 2 uses Intel’s XMM 7262 modem, which combines an Intel X-GOLD 726 baseband with an Intel SMARTi 4.5 transceiver. Built on a 28nm process, it features support for GSM/EDGE, UMTS (WCDMA, TD-SCDMA), and LTE (LTE-FDD, LTE-TDD), but lacks support for CDMA2000. Intel’s modem can aggregate up to 40MHz of bandwidth, delivering Category 6 LTE performance (300 Mb/s down and 50 Mb/s up). WCDMA performance tops out at 5.76 Mb/s up and 42 Mb/s down.

The ZenFone 2 comes with a feature rarely found in North American handsets: dual SIM card slots. Slot one supports 2G, 3G, and 4G standards for voice and data while slot two supports 2G voice only. The slots are Dual Active, meaning you can have two different phone numbers active at the same time (slot two utilizes the Skyworks antenna switch for the additional GSM support), useful for using a single phone for both personal and business use or when traveling abroad.

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  • wtfxxxgp
    I like the look. I love the price. Seems like a gem of a phone if good value is more important to you than the latest and greatest tech. I wonder if it'll be available here in South Africa...
  • manitoublack
    Great to read this review of someone doing something different.

  • MasterMace
    2 things that ding the phone before it even started: locked battery, 1080p screen. The LG G4 and Galaxy S6 both have 1440p screens. The LG G4 has a removable battery.
  • edwd2
    2 things that ding the phone before it even started: locked battery, 1080p screen. The LG G4 and Galaxy S6 both have 1440p screens. The LG G4 has a removable battery.

    Yeah, but the G4 and S6 also cost a whole lot more. Not to mention that the G4's A418 has trouble powering that 1440p res while the G6430 is just fine with a 1080p screen.

    And what does LG have to offer in the $200 price range? The LG G-Stylo runs a crappy SD410 and 720p display.
  • g-unit1111
    I wish we'd embrace the concept of dual SIMs and unlocked phones more here in the States. This is a very nice phone for the price and more carriers should be able to use it, right now it seems like only AT&T and Verizon can use it, leaving T-Mobile and Sprint out of it.
  • PC98226
    Great review. I was looking for your comments re: this device's ability to maintain wireless connectivity. I have been using the 4GB version of this phone for several months now. While I found it to have a VERY snappy speed, I experienced some quirks re: it connectivity. I would frequently have to check why the phone stalled trying to open up a web site only to realize that it had switched the connection from my WiFi to my wireless printer. This happened so frequently that it slowed me down re: productivity. I suspected there was some type of software glitch that needed to some attention. So, until that happens, I have returned to using my Moto X (2014). During your testing of this device, did you see or experience anything like the above?
    I own one of these, and I really like it. Asus has been very good about pushing fairly regular software updates, much faster than any carrier. For a time, it seemed like updates were hitting like clockwork about every 2 weeks.

    However, the one downside to this phone is the *massive* amount of bloat. The author touches on it a bit, but did not convey how much pure crap resides on this phone stock.

    However, there are many fixes available to that problem. A quick google for debloating scripts will get you headed in the right direction.

    My only other gripe is that mp3-based notification tones don't seem to consistently stop if you like touch the screen, or acknowledge the notification, you can't flip the phone over to silence it like on the Galaxy series. But these are minor nits.

    I get a full day of usage out of my battery, the quickcharge is nice, and for 300 bucks, the extra features of the other phones aren't appealing enough.

    I recommend this phone to anybody.
  • PC98226
    16526515 said:
    "....However, the one downside to this phone is the *massive* amount of bloat. The author touches on it a bit, but did not convey how much pure crap resides on this phone stock."

    Yes, I totally agree re: the massive amount of crapware pre-installed on this device. I tried to either uninstall or disable all that I could (nearly 33 apps in all) before I installed the apps I wanted to use. Now, these apps no longer auto-update so that is a help.

  • GoZFast
    I owned this phone from newegg since late May and I have to say that its the best phone I have ever had over LG, Samsung, iPhone, Blackberry etc The kernel is 64 bit but not the OS. Asus are working on a completely x86_64 Intel OS based on Android/Linux source code. Some apps are not x86 compatible yet but when they are, they run much more efficient than ARM. Its price of 299$ for the top 4Gb RAM model is too good for what it offers and if you even want more, you can join ZenTalk beta forum. With beta firmware, the phone is faster and battery lasts longer, never had an issue with beta firmware so far. This is also the coldest phone I have had, much colder than G3 and G2. Anything over 1080p in a 5'' device is pointless and will just consume more battery, create more heat and put a high load on the GPU. What also amazed me is that you can run 128Gb SDcards EVEN if the specs says 64Gb (Lexar 633x) The 18W 9V2A charger is faster than Samsung's 9V1.67A adaptive charger. Here is my newegg review, basically, the Atom CPU beats the SD810 and S6 in single threaded performance (Floating-point and Integer), it only loses in multithread (Hence, higher Antutu score) because its rivaling 8 cores so imaging doubling this in a future phone! I also doubt that playstore apps will take advantage of 8 cores like Anututu and hence, their higher score doesn't mean that 4 core or less apps will be faster. Intel can easily add more cores with 14nm but other are already 8 cores with 14nm and it will be very hard to increase performance with more than 8 cores. Intel Core M with Intel GPU in tablets is 3.5W while the Atom is 2.2W. If Intel can find a way to integrate it into smartphone, it will be a heck of a phone considering that it gets ~3000pts in PassMark similar to Intel Core i5-3317U or an AMD A10-5757M.

    Pros: Intel 64bit 3D 22nm Quad 2.33Ghz
    4GB Ram, did I underscore its speed?
    This outperforms all current cellphones (yes, faster than snapdragon 810) and have lots of headroom for improvement on intel architecture with more instruction sets for programming. We will probably see this device quad boot; android:windows:linux:mac os x
    Lots of potential.
    9v 18w charger! Higher than 12w ipad lol

    Cons: PowerVR G6430, same architecture as iphone 6+ but this intel extracts more gpu power vs dual-core 1.4ghz apple.
    Wish it had intel graphics which is up to 4x more powerfull than Adreno 430, highest current mobile gpu. Intel graphics would also throw more compatibility and instruction sets into the table.
    14nm and 3200mah maybe?
    Camera could be better (4k?) but not a fan of photography, it does what it says.

    Other Thoughts: For more battery life, put screen into reading mode and dim it as the default setting is very bright. Also, there is option to powersave in settings. You can also remove unnecessary apps, use system app remover for system apps (Not needed with Beta firmware) Getting better battery than my old g3.

    p.s: With beta firmware, you can disable/uninstall any app you want, even system apps without root. Root will break OTA and live beta updates. Many of these apps are actually useful though. Also, I found that Nova launcher decreased RAM usage by 80Mb and its snappier (Doesn't need root)
  • fyend
    Asus rivals Samsung with the amount of uninstallable crapware they preload on their phones. If you're planning to root, that's fine you can remove it all, but if not you're stuck with a lot of junk.