I really like my Gtech Comp, I also still have the old Gtech Pro. The Gtech comp is very accurate, with times and speed differentiating only +/ - .005 to .01 in comparison to time/speed at my local track.
The Gtech pro is out +2to3 mph and .1 to .2 seconds out.
I find the Gtech Comp. invaluable, when it comes to testing mods [what works, what doesn't] and also in finding out ideal shift points and launching. I've used the old Varicom[cost me $1300 bucks 7 years ago] for years when I was snowmobile racing, and I find the Gtech to be much better.