I have been diving for 7 years and I recently became a rescue diver. During the training, my buddies needed to inflate and deflate my bcd. Since I have air2, this was a problem. Not many people knew how to use my low pressure inflater. Usually, they just held down the purge. In an emergency, I want them to know how to use it. I know this should be gone over in your pre-dive talk but in an emergency, people forget most of what they know.
I think the use of air 2 should be covered more in your cert and rescue diver classes to help prevent this problem!
I was trained on buddy breathing and the use of an octo. I have since switched from donating an octo to donating my primary and wearing a necklaced octo.
I think you can use whatever you like provided your buddy is comfortable diving with you and your choice of gear. That being said, you have to accept that even if your buddy was trained on an AirII back when (s)he took their OW, if they aren't using one themselves, who knows what will happen in a serious emergency where you are incapacitated?
One of the things I like about going to primary donation is that even people who have no idea how it works use it naturally under pressure. They need a reg, there's one in your mouth, they help themselves! If you do not dive with a perma-buddy, I think the safest thing is to adopt gear that is familiar to the widest variety of divers, regardless of what training they "ought" to have received.
When it comes to suit inflation, I think the safest thing for you is to have a system that "just works" given a diver who forgets their training on your gear or has never seen it before. There's a lot of room for you to optimize your gear given this simple dictum. You can dive a wing instead of a jacket, you can do primary donation instead of donating an octo. Your hose can be 7', 5' or just 40". You can sidemount tanks, whatever you like.
JM2C, I have never been incapacitated on a dive, so I can't say for certain I have a system that is idiot-proof...
.
