Been using clipless pedals for over 8 years now. Shimano SPD(& it's copycats), Look KEO, Crankbrothers Eggbeaters and Speedplay X/2. Never had any problems with Shimano SPD; either SH51 or SH56 cleats. I only unclip sideways; so I can't even tell the difference. After a few years with SPD; a club member gave me his old Look KEO. I was so used to the double sided entry with Shimano; I had a hard time with the single entry KEO. Releasing was not a problem. It's getting clipped in; I wouldn't recommend this in heavy traffic. Plus the cleat will stick out ofyour shoes; making walking difficult.

Titanium Xpedo R Force pedals with Shimano SPD cleats(cant remember if 51 or 56):