I have both sizes of the razor edge knife clamps/guides. I was interested in this system because I had a large collection of bench stones (DMT and Arkansas) that I didn't want to abandon for a rod-guided sharpening system. I also prided myself on my free-hand ability with a bench stone, so the razor edge system seemed to complement the grinding style of bench stone sharpening. If you have bench stones already, the clamps are cheap and work well.
The razor edge system works best with blades that are 4" and shorter. Long blades require repositioning of the clamp. I use the small guide far more than the larger guide.
It takes some practice to get the clamp adjusted and in the correct spot on the blade but once you figure it out, you can grind a constant-angle edge. The guide/clamp also gets ground on the bench stone and slowly wears away, but you will learn to put more pressure on the knife edge and let the guide just glide on the stone. I've had mine for 10 years and they are still good.
I separate sharpening systems into two basic types: fixed angle systems (razor edge, Lansky, Edgepro) and free-hand systems (sharpsmaker, 1" sanding belts, paper wheels). The difference comes down to precision. The fixed angle systems grind a constant angle/edge with no rolling. With free-hand systems there is a tendency to alter the angle with each pass and the ground edge becomes convex (rounded). I use a sharpsmaker, paper wheel, and 1" belt system for kitchen knives and a quick touch up on my EDC. The sharpsmaker is quick but requires that you hold the knife vertical as you swipe it past the rods. I use it for knives that get abused (kitchen cutlery) and workbench fixed blades. For expensive, hard steel personal carry knives, I use the razor edge. It take more time, but you get a better edge. The razor edge is the best for reprofiling.
One criticism with the razor edge is that the angle changes each time you sharpen because it it not possible to position the clamp in exactly the same spot on the knife each time. This is true, but doesn't seem to be a big problem. I watch the grind (using a jeweler's loupe) and if the guide is wrong you will see that the edge is not getting touched. Some people use the felt pen marker on the edge to see this.
If you have some bench stones already, I'd recommend getting the razor edge clamps. The "kit" they sell is sort of disappointing because the so-called hones are really a block of wood with peel-n-stick sand paper that you attach yourself to the wood block. If you are looking to set up a sharpening system from scratch, get the diamond Lansky.
