I've used the Air 2 (and the Tusa clone) for many hundreds of dives and have never had a significant problem with it. I once had a buddy with a total OOA incident at 100 feet which required me use the AIR 2 for real. She used my short primary reg. It was absolutely no problem.
I also like the speed at which it delivers air to the bc, which seems a lot higher than other standard inflators that I've used. For the type of lobster diving I do in strong currents, it is very beneficial to be able to dump all air from the BC and get yourself 8-10 lbs negative which allows you to work on the bottom and catch bugs without a lot of finning or other motion. After the bug is in the bag, it is nice to be able to very quickly re-establish bouyancy contol as you leave the lobster hole and resume a neutral drift above the bottom.
I think the primary benefit of the Air 2 is that the diver is constantly handling it to inflate/deflate the BC and when the time comes to actually use it to breath, there is absolutely no problem in locating and deploying it. It is also, so very simple to practice with it, since you can just use it on ascent and when done spit it out when reaching the surface. No need to re-stow it.
Lastly I use a pony bottle, so I'm already dealing with 2 standard second stages, I don't want 3 if I don't have to.