Can someone please tell me what the difference is between RCS mains
sockets with active control circuits and those which are passive?

I was looking at this MK one for our garage:

http://www.mkelectric.co.uk/products...0&rangeid=1030

It has a 30mA rated tripping current. There is also a 10mA version. I
am right in guessing that the 10mA one is better because it is more
sensitive to any residual current?

Many thanks for your help.