Mmmm...It's interesting how many people hate their Air2. I have a Genisis Gemini Air2 and yes it can be bulky at times but I do like it better than the octo. The thing with Air2 is this, you have to buy it for a different reason than most people think. I agree that as a buddy sharing device it's not the best. I bought my Air2 because it's just for me in case my primary fails (it is not for my buddy in an out of air situation).
What do I use then, simple...
I always dive with a 40 cuf. pony bottle with its own regulator and SPG. If any buddy needs air, they're getting that one. The Air2 is there as a fail-safe to a fail-safe for me and it's streamed lined. I couldn't imagine having an octo and the pony bottle reg. If you dive with a pony bottle, I say the Air2 is fine. If you don't dive with a pony bottle, get yourself a regular octo.
Though I've never tried it...my instructor says that when ALL ***** hits the fan and your buddy is too far away, you can actually suck out the last bits of air out of your bc to reach the surface quickly yet as safely as possible..........of course he's also said that if you put yourself in that kind of situation to begin with...........you deserve "it"....and by "it" he meant death.