I was in the 2010 Jackson Star for the last 5 years, just cracked it a few weeks ago and decided to try the Jitsu 5.5. So just the smaller versions and here is what I noticed...
The Jitsu 5.5 outfitting is much better for me. I'm only 5 ft tall and the happy feet in the Jackson did not work for me. It would slide around b/c there was so much space in the front of my boat. Had to switch to regular bulk head. That worked but would have to adjust frequently.
The thigh braces in the Jitsu are much more aggressive and more comfortable.
The Jitsu was a bit more narrow on the top so my thumbs are not hitting the sides of the boat nearly as much.
They seem to paddle pretty similar, but I haven't had a chance to take the Jitsu out much yet. I personally think the Jitsu is a better boat comfort wise, especially if you are smaller. I did enjoy the Star, but am happy that I made the switch.