No. You only get a bit of extra damage. Critical damage is not worth the perk because of the way it is calculated.
WRONG.
I don't know the answer, but this seems like one that wouldn't take long to test yourself.
You are right. I tested it myself. The perk add a special move, where the character does a running jump attack through the air. It consumes allot of stamina, but it is really cool. I love it.
You should try shield charge. It's really lots of fun.
I know! It is allot of fun! Great perk!