I sharpen mine with a 10" single cut bastard file, by laying the file on a work bench, handle away, then set the head pointed straight down the file, maintain the same bevel, very important, and push the blade into the file, using light pressure. Rotate from one side to the next. If you keep the same bevel, you will soon have a blade with a burr, that can be removed by stroping on the back side of a leather belt. Once the burr is removed, you can use a 6" file, and draw the edge of the file, from the center of the head to the outter edge and from back to front in one motion. Done very lightly a couple times puts a fine serrated edge on this head, that will cut through a leather belt easily.
I am sure the KME Knife sharpener will do a superb job on this head, as well as some of the others methods. They might even be sharper, but I only need to carry one file in the field for a variety of heads.
The most important thing is to maintain the same bevel; if you use a file and file the edge the normal way, it is hard to maintain the bevel, the file rocks over the blade, rounds the bevel and leaves a dull blade. That is the advantage of the KME Knife sharpener for this style head, it will maintain the bevel on the concaved head, or a knife blade. Flat blades are even easier to sharpen, the way I have described.