I find most lightweight spd shoes for MTBing arent walkable enough for me to move through unridable sections of trail. I usually need to get off my bike and hop across a big puddle or climb a steep rocky section that is too steep to pedal through at least a couple times each ride. I ended up choosing the shimano sport shoe with the 3/4 hi top and I appreciate the support it gives me when I need to hop and climb. The sole is a little more flexy than your average racing shoe but still pretty stiff. Best of both worlds for the non-racer.