A530s: Normally come with the single release SH51 cleats. They have a flatter non-SPD side although with some grip and are probably better suited if you plan on using thinner soled normal shoes.
M324s: Normally come with the multi release SH56 cleats. These have a rounded serrated edge to the non-SPD side and offer more grip so are better used with thicker soled shoes or trainers or if you are likely to use the bike off road not clipped in.
I have both on different bikes and much prefer the A530.