"I have not seen the corner grip on the handle before. I have used the center grip / flip over into the deltoid smack for the cleans, what you describe as the powerlifting style. Any value to toughening the shoulders with that, or is it offset by the energy efficiency gain with the corner grip / twist around?"
Well, I'm sure it would toughen you up, but honestly, it's too much abuse for fighting. Bruised forearms don't heal fast enough.
The grip is the limiting factor in kettlebell lifting, from what I've experienced due to technique, not due to the implement. The way Pavel teaches it - the "death grip" - is all about his "inefficiency" premise - more tension. Our grip gets plenty of work just in clinch and ground fighting, so we use kettlebell training more for the power endurance effect (as well as isometric endurance of total time under tension.).
Pavel teaches the rack for some reason like you're constantly arm-wrestling (wrist curling) the weight, which is damn near impossible for time. But with Valery's "corkscrew" technique, managing to last 10 minutes seems possible (not all the time.) Valery's "angled" rack rests on the ulnar bone (the "hip" of the hand as Valery calls it), elbow to hip, locked knee, foot to ground - so it's mostly structure.
It's supposed to rest mostly on "B-C-D" (the "hip" of the hand) below:
When I used to try Pavel's techniques (I was a member of his first kb semmy) for 10 minutes, I'd be forced to break them into sets because of the grip and forearm abuse. But when we use Valery's techniques, we can prevent unnecessary abuse and focus on pushing our lactic anaerobic threshold (not limited by grip and forearm abuse.)
I think that they just wanted to develop a technique for minimizing damage and maximizing performance numbers within the 10 minutes, so their techniques are like surgery - minutia in there that I'm still learning.
I don't know if that addressed what you were actually asking.
"I was expecting more of a deep squat on the jerk, the vid looks like more of a push press. Mind you, I am pleased with that as the plyo nature of the jerk squat is hell on my knees."
Maybe I don't understand push-press in the same way, but the way I see push press is using a single dip to shove the weight to elbow lockout, and a jerk as using the single dip to shove the weight just high enough to make it weightless, and then a second dip to drop under during the free-fall to get elbow lock so structure then stands to elbow and knee lock-out.