I was running M530's before, still have 2 battered sets of them in my 'cycling toolbox'. I didn't exactly have any other comparison apart from when I changed to SPD-SL which were obviously a more secure & solid fit!
Got Keos on the summer bike, but the winter one has MTB SPDs, partly because of the 9 sets of lights on my commute and partly for the pre-existing 2 bolt winter boots.