I haven't made any good experiences with such Wifi drives
first of all, I've tried several SDHC-Cardreader with Wifi, on iOS much too unreliable and slow, on Android a little bit faster. Next try, an Intenso harddisk Wifi drive, seems to be the same App. Transfer is faster, but, settings of the App is a real desaster, no one of my friends would be able to set up such a drive, you have to be a network expert! Downside two, if you have copied large picture folders on it, say, hundreds of jpegs, you have to wait very long, to view the thumbnails, and going back through the folder you have to wait once more (on the iPad app). Doesn't matter, how far the drive is laying around, two meters or two centimeters, the connections aren't that stable. In the end, I use it only over USB on my Mac. All in all, much too slow and unreliable!