He's like hart in that he seems to have arrived very young. Apart from that, as others have said, the Hart levitational sideways leap was unique, although Petersen's mark last week was Hart-esque for Hawforn.
I was at the dome for the first time last Friday. If Jack maintains this form, wow, the mind boggles. He's very good at a lot of things, Leap, leading under, contested, roving a pack, the lead, the clokey-like arse-bump, and a big one for me that I've only ever seen Buddy do, maybe Richo at times, rove a spilt ball from a pack that he himself has crashed. He was amazing last friday, you knew he was gunna take the mark regardless of the situation, and they were tough situations that he was able to manipulate to his advantage.
Oh and as rT said, he's one grab, gold.