Thanks, shadows!
CleanMPG.com is one of the sites containing a lengthy thread reviewing the Ultra Gauge that helped decide me to try it out.
I received my Ultra Gauge in good time. It was easy to install in my '02 Grand Prix and there is a large selection of gauges from which to choose. The values seem accurate for the gauges I have tried - I used average MPG and instantaneous MPG to assess my driving.
After exactly one week of driving (5 hours run time, 180 miles), I have 26.3 average MPG on my 3.8L 2002 Grand Prix GT (non-supercharged). It's a very good product. The lighting changes with the environment - never has it been a distraction from my night and day driving. The suction cup for the windshield is of good quality as well - however, I placed my Ultra Gauge elsewhere to lessen the chances of theft.