I use my G-Tech a fair amount for 0-60 runs. I've brought it to the drag strip a couple of times to compare ETs and trap speeds. ETs run 0.1-0.2 sec slower than the time slip, while trap speeds run around 2 mph faster than the time slip. This is explainable: the G-Tech starts timing once it senses that you're moving, and it stops once its determines that you've traveled 1/4 mile (by double integrating your acceleration). On the strip, however, the ET clock doesn't start until you pass the sensor just in front of the staging sensors. So, you're already moving once the ET clock begins. As for trap speed, the G-Tech just tells you your instantaneous speed at the 1/4 mile point, whereas trap speed at the track is an average of your speed before and after the finish line.
So, the bottom line is the G-Tech provides fairly accurate results, and what errors there are can be easily corrected because they're fairly repeatable. The biggest thing hindering utility is finding a flat enough (and unused enough) stretch of road. I find dyno mode to be fairly useless because of the effects of drag, the inability to find a nearby flat stretch of road on which I can wind the car out at least through 3rd gear, etc. In short, the dyno results cannot be compared to a chassis dyno.
Is it worth $129? Shoot, compared to other stuff for the Viper, that's virtually free! Yeah, the flexibility of extremegeez would be nice, especially for a physics ****** like me, but it does cost a lot more (and unless you're going to write your own post-processing software, there's additional $$ for their full-up software, I believe).
