I use DMT Diafolds in fine (red)and just bought one for my daughter’s boyfriend as a Christmas gift. Light, effective on all steels, including S90, and a good handle to keep your hand away from the blade being sharpened. You won’t be disappointed.
The commercially available sharpeners seem to be overkill to me, especially the worksharp with it's 2 diamond grits, 2 ceramic grits, the guide system, and the strop. I don't need a guide, don't need ceramic if I have diamond, and don't need a coarse grit. A small strop is all that should be needed in the field. Just a piece of 1/4" plywood with leather glued on and treated with diamond grit will quickly get a blade back to shaving sharp if you don't let your blade get so dull it needs a stone.