I use SPDs, like others learning to use them was over before I clipped in and out the 15 times the LBS recommended, but getting used to them took a little longer. I also set the release to the easiest release and have never accidentally clipped out. Everyone told me you'll fall soon after getting them but I went two years without falling until riding on some trails that had 12" plus deep patches of sand and it was ridiculous. Probably fell 10+ times that day but the sand made it mostly a soft landing.

I really like them when trail riding I feel much more in control of my bike and like that I won't lose contact with the pedals unless I want to. Mountain biking shoes make a big difference for comfort. I can walk around pretty much anywhere in them. I bet there isn't a huge efficiency advantage for most people, but I most got them in the first place just to try to strengthen more muscle groups, so I didn't really care about the efficiency or carbon fiber shoes or that stuff.