I have used the original standard "g-tech" unit.
I have heard at worst they are a couple tenths and a couple mph off on trap speed.
I do not know if the quarter mile, speed, and 0-60 are exact but they are really close. Just a few tenths off advertized test numbers in my dakota, conquest and shelby.
The one thing I found is that they are very very consistant. I get the same numbers every time.
You cant beat that if you are testing to see if an intake, exhaust, timing etc has done anything to affect your performance.
You can get an original G-tech on ebay for $25.
For that price, who cares if your ET and mph are off a tick... at least the numbers are consistant every time.
Good cheap tool IMHO.
thanks