I ride SPDs on my mountain bike, but they have a cage around the clip. I need the clips for climbing, but I really like having the flats for technical stuff, near a cliff or anywhere I don't feel as confident. I don't see very many people riding pedals like mine, but they work for me.

The pedals I run have clips on both sides (just like regular SPDs). There are others that only have a clip on one side. I think these would be confusing for me. I would never know what side was up, and I would probably clip in when I didn't want to.

Clips require more TLC on a mountain bike than a road bike. The mud and dirt do cause havoc on them. You have to keep them as clean as possible, adjusted and well lubed.

I ride a pedal that works something like this: