All of these devices look like familiar USB-attached storage devices, and they can, in fact, be used like that. But they're all more functional. Their prices are a good indication of this; each product is notably more expensive than simple external storage.
Fortunately, USB connectivity isn't just a bullet point on the feature list of Seagate's Wireless Plus, Corsair's Voyager Air, and PQI's Air Bank. Thanks to compatibility with USB 3.0, they all achieve as much as 110 MB/s in reads and writes. Perhaps owing to its form factor and memory type, SanDisk's Connect Wireless Flash Drive is interesting-looking, but posts USB dismal performance as low as 18 MB/s.
The most interesting features we saw were probably integrated Wi-Fi and built-in batteries. Both features, taken together, let you create a mobile hotspot with wireless storage available to client systems. Put a drive in your backpack, and you're able to access a complete media library for any mobile device, wherever you are.
Corsair's Voyager Air and Seagate's Wireless Plus will even stream content to the friends around you, along with DLNA-compliant devices like smart TVs, Blu-ray player, and game consoles. The two PQI devices aren't as compelling. They don't offer Internet pass-through, so you're stuck facing a choice between online access and access to your stored data. You can't do both at the same time.
Enabling an easy setup and smooth user experience requires good Wi-Fi performance and a well thought-out interface. Each of these vendors provides an app able to run on modern mobile devices. But none of them achieve what we'd consider to be stellar wireless speed (the top option topping out at around 5 MB/s). That might be sufficient for streaming music or video, but you'll find yourself waiting on larger data transfers, to be sure. The exception is Corsair's Voyager Air, which you can plug directly into an Ethernet network and use as a NAS to achieve transfer rates as high as 30 MB/s.
Most of the app do what they need to do, but none of them have us particularly impressed with their creators. Two stand out in our minds: one for good reasons, and one for bad. PQI's uninspired implementation of the Air Bank+ software left us disappointed, particularly when it came to the app's multimedia functionality. It lists all songs alphabetically in a single folder, disregarding meta data. Once you have more than a handful of albums that employ similar naming conventions (for instance, a track number and song title), you're going to start losing track of albums in your head. Seagate, on the other hand, gives us something to praise. Its app lets you quickly sort multimedia files according to several defined categories, such as song title, genre, or artist, somewhat similar to iTunes.
The Voyager Air, Air Bank, and Seagate Wireless Plus each include an internal hard disk with 500 or 1000 GB of storage capacity, and hence are best suited to large data collections. Kingston's MobileLite Wireless, PQI's Air Drive, and SanDisk's Connect Wireless Flash Drive are smaller, lighter, and less expensive, but offer less storage flexibility; they rely on SD or microSD cards for holding your information.