The fine grade is ideal for router cutters, although they may benefit from a further polish on an extra fine version. Do clean the cutters before you start though, or you will clog the sharpening stone with resin.
Diamond stones can be lubricated with a little water, but always dry both them and the cutter after use to prevent rusting. Some people prefer to use thin oil as a lubricant on diamond stones, but there is now a specially formulated diamond stone lubricant which is much better.
To hone the face of the cutting edge, press it firmly onto the face of the stone and draw it backwards and forwards a few times, making sure it is kept flat at all times.
A few strokes should be enough as the diamond stones cut quickly, but remember to take the same amount off either side. Never try and hone the grinding angles