I bought a C12k but only because it was owned by someone I knew and it's twin was owned by another person I knew and both of them are experienced honers. Sometimes I can't quite get the edge I want off of one of my two cotis and so I'll try finishing on the c12k and more than half the time it kicks the keenness up a notch. In fact, my keenest edge was finished in just that way. Sometimes, it seems to make no difference. I would never buy one though from someone I didn't trust because of the reputed variability in their performance.