In reply to Jams:
I've never tried it whilst not doing other climbing too so I couldn't really say because I can't isolate the effect.
It certainly feels like a workout though.
Unlike cha1n I've never really found the straps in the way although maybe that's the choice of exercises. Also I don't think I could get the rings low enough to the floor to do some of them off the rings at the wall. I also found I preferred core exercises on the TRX to a bar for some reason, not sure why.
You can also make trxs for a pittance from rope offcuts whereas I don't know there's a super cheap source of wooden rings, if that matters...