The DMTs mini sharps are reasonably good, but I do seem to have trouble sharpening ZDP-189 steel (HRC of 65), which is very difficult to sharpen. I seem to get better results with a cheap diamond rod sharpener (powerfix) I picked up from a local discount store for about $4. It looks to be identical to the Gerber Sharpener available here;

http://www.amazon.co.uk/Gerber-09841-Diamond-Knife-Sharpener/dp/B0001WOTHC

Using the Powerfix Pen diamond rod and a Red DMT F70F, covers most needs.