So I just tested this out. Not crazy about their implementation:
1) The AirPlay stops if you switch to a different app or turn off the phone display. Worried this will be a battery hog. See Plex for how to do AirPlay right.
2) The picture quality sucks. Like VHS quality. Well, it starts off sucking really badly, and then after a minute or two it seems to sharpen up, but it sometimes goes back to sucking again, and even at its best, it's a far cry from iTunes store HD. I'm not sure if the quality is worse over AirPlay, or if it sucks just as bad when watching it on the iOS device itself. I used an iPhone 5 and I think it looks pretty bad on the iPhone display as well.
I suspect that this will be "better than nothing" for the occasional show I may want to watch that Amazon Instant is giving me for free (I'm a Prime member), but I certainly wouldn't want to watch an HD action movie with it. YMMV. If you have a small TV, then you may think the quality is fine.