Matt - I think the belt you're referring to is a torso belt - Racerwholesale sells them. I think they are fine for autox. I'm not sure I would use it for track though.
http://www.racerwholesale.com/catalo...roducts_id=195
I thought about getting one to keep me even tighter in the seat, but decided against it due to my seat's contour - didn't think it would help that much since the sides of the seat are bolstered, plus I didn't want it to interfere with any airbags.
I find the 'seatbelt trick' holds me in very well, and figured it was better than the CG Lock also, which only tightens down around your lap - not your upper body. I'm not sure I understand the reasoning behind the CG Lock. I know I can drive better with a harness since my upper body is stable and I'm not using my grip on the steering wheel to keep my upper body from flying around. That's why I still want that feeling of being fastened down by using the seatbelt trick, that I don't think you get with a CG lock.
For track -- I would look into the approved harness recommendation and understand what its pros & cons are - but as others have said, the final decision and the responsibility for your safety based on your decision is still yours.