For several reasons, most to do with compactness and durability, I have chosen to use flat diamonds exclusively.
Thing is, they're real poor for doing concave edges. The only way I know to get any results at all is to get the diamond stone of it's wood base(which I do anyway), put it up against the corner of a table and sharpen on the the upper edge/corner of the stone.
It works, but not real well. That concave edge is what kept me from getting a 710 even though I more or less like the knife otherwise and do need a new folder as I broke mine.