My husband had tons of problems with his Polar on his roadie, never used one on the mountain bike. He now uses the Garmin Edge 500 and we both have had very little problems on the trail. He has the HR and it doesn't cut off if his gets too high but the Polar did. I walk a lot with mine and it always catches the bike is moving. It tells you moving average speed and total average.
Amanda
2011 Specialized Epic Comp 29er | Specialized Phenom | "Marie Laveau"
2007 Cannondale Synapse Carbon Road | Selle Italia Lady Gel Flow | "Miranda"
You don't have to be great to get started, but you do have to get started to be great. -Lee J. Colan