Congrats on your Rescue Diver cert... I’ve seen this airtrim setup in the past but I’ve never had experience diving with it.
In the dive industry, it is not unusual to see the occasional innovation. Something that alters the "standard equipment configuration" (if there is really such a thing.
In my opinion, here is what you might do. First of all, every time that you dive, you and your buddy should be doing a pre-dive. In this pre-dive, you should be making note of their equipment configuration (including such things as weight release mechanisms, BCD inflation systems, accessories, etc...)
If there is something about your buddie’s rig, you should work out how you are going to handle an emergency, before the dive...
Another thing you might do is to get in to the pool and go through every emergency situation that you can think of and practice how you can best handle the situation.
Then, while in the pool, let another diver use the same configuration (in your case Mares Airtrim) and practice how best to deal with helping another diver who is using that same configuration.
It appears that you have learned one of the most important lessons that up-and-coming rescue divers, dive masters, and dive professionals all must learn, during your experience. That is, not everybody uses the same equipment, so you need to be aware of the different variations and become familiar and comfortable with the techniques that work best in the different situations.
This is not an easy task, but the time you spend working on it is well worth while.
Again, congrats....!
Safe Diving
Ron sends