I have Shimano 520s and 540s on my road and SS/Fixie bikes, but my Trek 520 has Shimano M424s. They are essentially Shimano 520s with a cage around them. I clip in and out easily but can also ride comfortably with sneakers if I choose to. I have over 1000 miles on them and they're still in great shape. Good price too. ($28.99 at Nashbar right now)