The Intamin T-bar is much more comfortable than the shitty Arrow lap bars that'll basically destroy your thighs if you don't tighten the seat belt well enough.
The deal with the seatbelts is quite odd. Some seats on various rides have very short belts for whatever reason; belts which, at maximum length, don't give as much free room/slack as you'd expect even for someone skinny like me. I would guess that someone who's large and tall, but not necessarily fat, could have trouble with them. I wouldn't know though.