If you're a wrong'un SPD pedals are prone to misclips that then refuse to let go of your foot, and may be shit if any kind of earthy substances contaminates the pedal or cleat but being steel you can easily smash any crap out of them.
My old Nike ACG shoes had the original SPD cleats on them. fade to fond memories
My old Nike ACG shoes had the original SPD cleats on them. fade to fond memories