Network Performance
When the Voyager Air plugs into an Ethernet network, it wins sequential read and write benchmark hands-down. At 31 MB/s, it even serves as a respectable NAS appliance.
Connected wirelessly, Corsair's drive is still second-fastest in our write test, though it falls to third place in reads. Kingston's MobileLite snags the second-place spot by achieving 5.1 MB/s. Seagate finishes last at 2.5 MB/s (for reads) and 2.6 MB/s (for writes).
The PQI drives and SanDisk's Connect Wireless Flash Drive do not support the SMB protocol, so CrystalDiskMark is unable to generate results for them.

USB Performance
When you pit USB 2.0- and USB 3.0-based drives against each other, the outcome is pretty obvious. The three devices equipped with USB 3.0 connectivity, Seagate's Wireless Plus, PQI's Air Bank, and Corsair's Voyager Air, achieve almost identical results. Kingston's MobileLite Wireless and PQI's Air Drive offer typical USB 2.0-limited performance. Only the Wireless Flash Drive seems stuck somewhere under the interface's practical ceiling, particularly in our write benchmark.

Six Battery-Powered Wireless Storage Devices, Reviewed : Read more
I can see the utility of the wifi hardware for peer-to-peer connections ala AirDrop, but I didn't see that mentioned as a feature on these.
Buy the 500gb models and wash your hands.
http://www.hypershop.com/HyperDrive/iUSBport/
very useful for in the car/when traveling, each devices connects automatically, the kids even learned how to find & navigate the apps on their own.
Then I simply take the device with me when get to the destination (i.e. mall/park/etc), and they can resume watching while eating lunch, resting, etc.
I think these are aimed at multi-user families.
I have a NextAV D100 wifi drive (not reviewed here). I can tell you it is quite handy when you travel. 1. The battery can charge your phone. 2. You can carry a lot of movies and music so you can watch and listen for long trip. 3. Backup photos and videos. The drive I have has a SD card slot and a USB port. The storage of the drive is provided by the SD card you slot into the wifi device. The USB port is where you plug in to charge your phone and where you can plug a HDD so you can backup things from the SD card from your camera or camcorder into a HDD.