I got the Worksharp KTS as my sharpenings system, and found many more uses for it than sharpening. Shaping material, grinding gemstones with aftermarket diamond belts, etc. For sharpening, it is excellent. It is good if you have an intuitive sense of how sharpening works and how belt sanders work. This gives a convex edge. I re-configured mine to be portable, and able to be attached to a DC power supply (analog variable speed essentially), so overheating isn't an issue, but people have brought up overheating the knife edge as a potential hazard, which will ruin the heat treat. If you go this route, I can't stress enough that you should test it out on a cheap knife first. It removes material very quickly, and if you try it with an expensive knife you could ruin the edge, scratch the blade, etc.
WITH THIS SAID, I highly recommend the Spyderco sharpmaker, even though I never got the hang of it. I tried the sharpmaker on a recurve knife to start, which was a terrible idea. I ultimately failed at freehand sharpening, and ditched the sharpmaker, only to realize that my bevel angle was steeper than the sharpmaker angle, which was why it wasn't working. If you can get the hang of using a system like the sharpmaker, that is the ultimate in my opinion. No batteries or outlets needed, just you and your skills. Unfortunately, I apparently have the hand eye coordination of a giraffe when it comes to freehand sharpening, so I had to go with the powered solution.
With enough practice, you can make either system work.