echoing what andy says but also i found they ended up making my knees ache. had always been a shimano pedal man but then when they first came out i got them, liked them so then fitted out most of my bikes with them, including the road bikes.
basically i didn't notice initially but where they don't support your foot aswel as a shimano pedal i found that when i pushed hard on the pedal my foot would lean over which meant i was pushing down with my knee in a slightly angled position which after a while caused issues.
back on shimano now, no issues with my knees, also the cleats last so much longer and don't ruin shoes and the bearings in shimano pedals last so long by comparison with smegbeaters.
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