I bought a Scangauge about two weeks after I got my Yaris. Pre Scangauge I went from Reno to San Leandro (230 miles) and averaged about 41.5 mpg. With Scangauge the same trip was 48 mpg. Traffic was a little worse the first time I admit.
Before the Yaris I had a '94 Metro. I just wish I would have tried driving the Metro using my new FE skills taught by the Scangauge. I was getting 52 mpg in it before, maybe 60-70 mpg would have been possible.
I am a believer in the Scangauge. So far 5 people I know have bought Scangauges after seeing mine work.