I use PD A600 on my roadbike, and did have a pair of A520s. (similar) They are one sided, but have a platform around them. Because they are all Shimano SPD I can wear any of my shoes on any bike. They do impart more power and I don't suffer hotspots. M530s are a bit heavy for road use.
The cages on the PD M530 do touch your shoes and give you a bit more to push on, but for me it's the fact that you have something to pedal against if you don't clip in first time. I actually uses M545's on my trail bike, but am saving for some M785 XT trail pedals. (£48 at
Ribble)
The reason I recommend them is because A520 are great pedals, but if you can get the M530 for less than a fiver more with cleats it's an absolute no-brainer.