In reply to Ben Watts:
Ive tried both, I preferred the socks because they also supported the ankle, however that then limits you to wearing that particular sock, the calf guards allow you to wear any socks you like so are more flexible and not needing to be washed as often may last longer.
I found that they do reduce muscle stiffness the day after the run but not by a huge amount, I certainly wouldnt go spending loads on these things, some are easily £40 which is daft/