I have ATAC Aliums on my moutain, cyclocross, and track bike. I've never accidentally unclipped them. I also wear mountain bike shoes with steel lugs up front, so the cleats rarely touch the ground. Next time I'll buy the more expensive Time's with the better bearings. The plastic dust cap on the end of the pedal spindle of the Alium works its way loose once in awhile, and allows the pedal to shift laterally over the spindle -- seems like kind of a design flaw to me. Anyway, I just wrapped teflon tape around the threads of the dust cap, and that seems to hold it tight. That being said, I really like the simplicity of the spring mechanism. Plus, if you want to increase the release angle, which I have not needed to do, you can swap the left and right cleats.