The only reason I use one is that I really like the controls on it better than the standard inflater. It is not comfortable to breathe from and doesn't breath well. But, if I was going to be using it, it would be to surface immediately so that doesn't bother me. Just my thought.
I have my AirII adjusted to breath fairly well or at least to do what I am supposed to do and that is to go up to the surface. I'd compare it to the Sherwood Brut performance.