Weird, my atomic ss1 breathes very much like my other atomic regs at depth. Like other regs, there are some air2s that breath great and there are some that breath poorly.
Also, if you're the casualty in a rescue scenario, the use of an air 2 is totally transparent to you. Unless you guys over there are training that the air2 is donated, in which case, this is a training problem, not an equipment problem.
Whilst the BSAC don't teach primary take. That isn't really an issue, I've trained with enough agencies to have done both primary take and secondary donate.
If your buddy only has an AIR2 and doesn't anticipate or has an issue, you may be forced into using the AIR2, so you better learn how to use it incase it's the only thing available in your hour of need.
I have limited experience of AIR2's, I've used them in training. I had one on the CCR during training and on my unit before I swapped it out for a dedicated regulator. Didn't enjoy breathing from them at depth, at least on the CCR below 20m I was always carrying a bailout stage.
I found during rescue drills that my head movement felt restricted, and the 'casualty' was far too close for comfort when they where using my primary regulator. Not something I would like to do 'for real' especially in a restricted environment like a wreck.
One of the nice things about the long hose is that you can give yourself some space if the casualty is panicking, not viable when on an air2. (It's also the nice thing about a bailiff stage, you can sort the casualty out with gas then hand off the complete stage which is nice).