Originally Posted by
surreycrv
It's the shoe, not the pedal, that makes for the efficiency. A carbon, or otherwise stiff, soled shoe will accomplish the goal. SPD's are walkable, so if you want to go into a store, pub, or even just a washroom without slipping, they're a better solution.
Some road shoes like Specialized have a heel made out of rougher material so when you are standing you are on the cleat and the heel and there's no worry about slipping. They still aren't that natural to walk in but definitely better.