Hmmmmmm.......
Okay, I grant that this is an interesting skill and idea.....but kinda hard to practice, isn't it? I mean, you have to get together with a bunch of dive buddies and hope that conditions are okay, or you have to make use of a pool.......
Ya can't just be practicing this stuff walking down the street, I'm sure....and the bathtub is a bit restrictive....
Peace--