I've never used the sh56 multi release. I've been riding the SH51 for about 13 or 14 years now. They are extremely easy to unclip. I just pedal up to a stop, and never worry about unclipping at the last second just as the bike stops moving. And in stop-and-go riding, I can just stomp and go without looking. Some of the other group riders need to look down before clipping in with their road pedals.

I did have the usual close calls the first year, either from an unexpected panic stop, or accidentally clipping in when I thought I was unclipped with the sole resting on the pedal. The only time I have any problems now, it's from a piece of gravel or a bit of a stick stuck in the cleat.