on my last trip, with a "boat buddy" I got on the ride out, I checked his gear thoroughly.
Good thing, too. He had forgotten to bring weights or weightbelt (I had an extra belt and we found enough weight on the boat). He didn't have a timing device of any type. He had a brand new BC (just rigged that morning), which he did not know how to use.
Prior to jumping in the water, I made sure his air was on (it was not) and that he had a good fill. I watched, he never even looked at his pressure gauge, and didn't see me check it.
I then showed him where my weight release was located and the positioning of my octo. "Why'd you show me that?", he asked. I explained, and he seemed satisfied.
I do this with any new buddy, although I don't follow a formal procedure or checklist. I may just look and see "how they are set up", or I may ask them if I have a question about what they are doing or a preference that they might have......
With my "reggler" buddies, I usually just ask, "You get a good fill? Didja fergit anythang? Let's go!"
Btw, after 25 years, I have missed things I shoud have done that a good buddy check would have caught. I once made an ascent to 70' in a wicked current while thinking, "Man, this is tough", only to realize I had forgotten my weightbelt. I have also back rolled off a boat in heavy seas without my fins (hey, the spearfishing was hot that day! We were excited..."
Anyway, all of us make mistakes, and buddy checks can at least mitigate some of them......