It’s not free diving if you have an air supply, I like your idea for quick shallow dives you should get some reasonable dive time, I would call it microscuba.Don't see it as much different from "monkey diving" as long as you continue to breathe from the pony on ascent or exhale all the way if you go OOA. I've just ordered a 19 CF to use without BC, etc so I can carry what I need for short shallow dives in places I can't get a full kit to. Basically fins, mask, snorkel, snorkel vest, tank and just enough weight to get down. I'm sure I'm not going to kill myself.