I wear the Murray's sit Racing harness, with a spreader bar, and no other keeper for the dogbone/trap line. It's also crotchless. It has the vertical batten-like strips paralleling your spine. It is soooo comfortable. It would be easy to get off in an emergency.

I have let many borrow it thatr have the full harness and they can;t believe how comfortable it is. I've been on the wire for hours at a time, no problem. IMHO, full harnesses are not more comfortable, are bulky, too hot in warm weather, etc.