whatever system you use, it really comes down to practice, practice, practice. I have used the AirII, but would rather have a plain old octo on my waist D-ring. The AirII is uncomfortable to breathe on for me, so I don't choose to use it. HOWEVER, since I don't expect everyone to wear my size bathing suit (it works just fine for me) I really don't expect everyone to be comfortable with my octo set up. Just like when you buy a mask or fins, comfort and fit are the most important criteria. After you determine HOW you are going to deploy the back-up reg you should practice, practice practice till it's second nature.
The most important points are to have a set system, share that system with your buddy, MAKE sure your equipment is functioning correctly, and then practice early and often!