Seems like alot back arch at the start....I mean, he does 'come out of it' right away and gets underneath, straightens out
But doesn't seem 'wise' . . . IMO
As far as his trick to initiate that stretch/reflex thing . . . not a fan of all the wiggling around right when you get into this arched position with a max load.
Would never recommend for anyone.
Lets figure out some way to bounce around and get a stretch reflex on the start of 1RM deadlift too...seems smart.