Ron, I hear you but I'm not sure its relevant. ... With that in mind, the Air 2 was by definition firmly in the "octo/air share" era rather than the "buddy breathing" era and hold over skills from the buddy breathing era have no real relevance to how trhe Air 2 was designed to be used.
DA Aquamaster,
My comments 1-3 above were meant to suggest that certain prior training made/makes adopting the Air II much easier, even if that prior training didn't/doesn't pertain specifically to using an Air II. For example, if that prior training leaves you extremely practiced and comfortable removing your primary (to, for example, buddy breathe or manually inflate/deflate your BC at depth), then adopting an Air II is much easier, I think. For another example, if your prior training leaves you extremely practiced and comfortable reaching over your shoulder to manually trip your BC dump valve, then you will naturally think of doing this (manually tripping your dump valve) as another option for controlling your buoyancy when you're breathing from an Air II, I think.
I agree, training designed specifically for using an Air II is (should be?) preferred for preparing someone to use an Air II. But, clearly (to me, at least), these hold-over skills from the buddy breathing era are still relevant. They can not only make adopting an Air II easier, but also leave you with important skills to use if the Air II fails.
Safe Diving,
Ronald