I use me Garmin Geko 301 on rides mainly to map out my route AFTER the ride is over, and then email it to friends. The unit is pretty small, ~.75x1.5x3 inches, and the handle bar mount works great. Sometimes I navigate by waypoints on mountain bike rides, but this is rare. I've found that the GPS odometer function is not as acurate as the standard bike odo type because the GPS tends to "cut corners" on the switchbacks (GPS acuracy is ~10-20 feet, which is less than some of the tight switchbacks on a mountain bike ride).