Hmmm, kinda cheap for a dyno machine. I didnt read all of it, but has anyone at least heard of the company before?

http://www.bahntech.com/products/Aut...OVMTC=standard

I use digimoto software for this and my lap top. Its hard to get accurate readings without an accelometer but if I leave it 2nd gear it will draw a graph.
The nice thing with the digimoto is you read many sensors in real time and will do quater mile times. You can also reset ses codes with it, not bad for a $100.

take a look here www.digimoto.com

That does the same thing as the Gtech Pro Comp. Only the Gtech will calculate lateral G'* as well.

how accurate are these things?

I dont know. I would geuss pretty close. I doubt any device out on the market for this price is going to be more accurate then a shop machine.