Hi Geoff
No, I've not seen one of these before, its looks quite interesting. With Garage Band for iPad being so reasonably priced, it seems a good proposition for people on the move.
Another option that may be worth considering is the Apogee Jam, which by comparison is very basic, but still opens up a viable prospect of making music on the iPad:
http://www.apogeedigital.com/products/jam.phpThis of course is input only through the interface, but I would think the headphone line level out should do the job.
Gary