When I first went clipless, years ago, mountain biking, I got the SH51, and would just fall over at the top of steep dirt/gravel climbs, etc. I just couldn't get used to them and was about to give up on clipless, then tried the SH56 and never turned back. I have never had a problem accidentally unclipping, and I am pretty heavy and strong and could torque the pedals pretty good (not as much nowadays though). Secure enough for me. YMMV.