I just bought one too. Also from REI. I've only used it once so far and haven't even set up the speed sensor yet, but I can tell you that the GPS based speedometer was dead on. It matched my current speedometer exactly.

Two minor complaints so far. The graphics seemed small. But I know I can change that. I had too much information being displayed one one page.

Also, not liking the unit's placement on the stem. I'm used to my speedometer being above the bars, as seen below. I may try and relocate it if possible.