Bought one of these earlier this year and tried it for the first time a few days ago. Looks to have a fast response/refresh time and is very accurate. So far only did some 30-90mph pulls as I came across a site with a massive list of cars for comparison (you can create any custom performance benchmarks).

Got a 9.55sec manual shifting, and a 9.42sec in DS mode. I Started the pulls in the 25-27mph range, so quite low revs second gear when beginning the run. Probably a few tenths more I can shave off trying different gears/shift points/starting speeds etc.. if I really want to.

All in all a cool little tool, especially useful in my opinion when tuning or upgrading your car and backing up the statement "It feels way faster"