G-Tech Pro RR?

I used something called the Dyno-Rad, which is the same idea except it gets it's speed reading from the driveshaft. Because I used it on the same car time after time, I would say that it worked excellently.
However, it has to be re-calibrated every time you change the rear gear or tire-size.
To get around that, I finally pulled the trigger on the SS. But when it finally arrived, my tuning was done and the rear gear settled on. So if you can't find one down there, I might sell you mine, new in the box, never used.
IMO an accelerometer is a great tuning tool.