I am slightly less incompetent than I was a year ago.
I rather think a CESA is what you do when everything else fails horribly but you are not dead yet. Beats drowning. I don't think the "horizontal" practice stuff is worth beans, and I am confident the vertical practice is stupidly dangerous if it is done widely. Take a freediving class if you want to get better being underwater without a tank. That's my plan when I get through my higher-priority courses.
Interesting topic though. I assumed CESA was to dangerous to be commonly practiced, and now I know even experienced divers think the same thing.