I mostly use shimano M520 spd. I have some of the more expensive spds but have decided that its not worth the extra money. Haven't had a problem yet except that one of the pedals was loose when I first installed it and made a clicking noise with each revolution. I needed to get a special tool to repair the problem (it was a couple of dollars only) but since I ordered it online it took some time to receive it. I was able to adjust the slop out of the pedal and it is working fine.

I am glad to get the tool to open the pedal, because I do all my own maintenance.

The 4 or 5 other pairs of M520's have been fine and worked well out of the box. I think this problem was an anomaly.