One of the most popular dual sided SPD pedals on the market. In production since 2004, this pedal is so good it doesn't need to be changed. Compared to the M520, the M540 is lighter and has a more slender spindle without wrench flats for a cleaner aesthetic. There isn't a difference in binding and release performance as they are both adjustable but the bearings are of higher quality in the M540s so may last longer.
A great option for long term touring, mountain bike days or easy commuting.