As with most coasters... it depends... but in my experience, who it will be most uncomfortable for are the very tall. The very large simply won't fit the restraints and will be told to walk. The very tall need to contend with the awkward leg restraints. I'm 6'2" tall and ~180 lbs and I found the restraints to be very nice.
The restraints are much more along the lines of FoP than Hagrids (even on the motorbike side of Hagrids, the seating is still mostly upright with the restraint being essentially a traditional lap-bar; people may lean forward to hold the handles, but the seating is still rather traditional). But unlike FoP, you lean much further forward on Tron and the restraints are better designed to cradle your body. The riding position feels much more similar to a flying coaster (just above the track) than a traditional coaster. Being forced to lean so far forward gives an enhanced feeling of speed.