I'll answer before he asks, I use the C12k, also know as a PHIG (Peoples Hone of Indeterminate Grit) Ans they are good, but they are a pig to lap flat. Once done though, you would rarely (if ever?) need to go back to it, and it would be easier the next time around, as you are already working with a reasonably flat face after the first lapping.
Keep in mind that I am the epitomy of cheap bastards, and I won't go out of my way to spend wads of cash on something that I see as going back to basics. I shave, it's not a hobby, it's not a chore, but it is a pleasure...Now!
Mick