16 years on MTB's and most of that time using M520 pedals. When I went road I found foot ache coming in with them though and as I did not want to have two types of shoes for different bikes- the LBS suggested the A 520's That cured the foot ache and so it is M520's on the MTB's and A520's on the road.

That longer platform gives more support to the foot- being single sided caused a slight problem initially but once the bearings wore in- it always sits right side up. On top of that- I can walk around in the spd shoes- that I would not be able to with Road type shoes.