I have one. Everything is perfect, long battery life, very easy to use, HOWEVER, the volume is complete and utter shite. If you're riding over 50mph, forget it.
Interphone haven't released a full set of instructions yet, so there's no way to turn off the speed sensitive volume. There may be a software update to fix this, so I'll be sending mine back for a refund unless the issue is fixed by mid June, when I'll need it for a trip.
I wouldn't recommend buying one until these issues are resolved.
Edit - full instructions are now on their website, so I'll play with the volume settings when I get back from the US later in the week, and update the thread.