It's the next best thing to having a dyno in your car. It's a little inaccurate, but pretty darn close. It really helps with analyzing changes in handling and acceleration. SOTP dyno sux, especially since you put as work into the new part you put on it almost always feels like it's better, even when the GTEC says no.
You can also find them on eBay from time to time... think of it this way. You spend what you spend on the GTEC, then put on your mods. If the mod doesn't effect the car as much as you thought it would, yank it off and sell it to someone else, you've lost a few bucks, but you've not been tricked into thinking that the "V6 mod chip" you bought on eBay was worth the $35 you paid! Trust me, I've had more than my share of unhappy campers begging me to remove the darn things.
They're better than spending 200 at a the dyno every time. But never rely on a single measurement from G-tech. Do several runs with it, and take the mean (Average). If you take just one number from a single run, it will not be seen as a valid number. But if you tell people, "I did 5 runs and this is the average that G-Tech gave me" then it will be accepted. :mrgreen: