Costa really brought the whole c-clamp grip thing to the forefront. And the AFG was originally introduced as part of their "theory" product line along with the BAD lever. People were absolutely obsessed with anything he was doing for a few years. It was ridiculous. Oddly enough, he abandoned the AFG and BAD lever on his own guns. Guess they weren't as useful as we thought.
He still uses the high wrist angle, straight forearm, c-clamp grip. I tried it for a short while in addition to handstops. It didn't work for me at all. Greater fatigue and not comfortable in practical use. I went back to my tried and true short VFG. It allows me a more comfortable 3/4 grip on the rail, better rearward pressure into my shoulder and more versatile hand placement. I think the c-clamp may be useful in competition, because it does seem to offer a little more control and with enough practice may offer better split times. That's fine when a stage lasts a few minutes. But it doesn't work so well after a full day on the range, with varying shooting positions, transitions, etc.
ETA: Remember when he was covering himself in tape? That was pretty entertaining.