It's ceramic, not carbide. I'm not planning to use it to set a primary bevel; just for quick touch-ups in the field.
The main drawback in these sharpeners is with the closed-bottom 'V' in the arrangement of the inserts (whether carbide, ceramic, diamond). It's a very hard dead-stop at the bottom, against which the apex (not just the bevels) will grind. If the held angle isn't perfectly consistent from one pass to the next, and pressure is just a little too heavy, it's almost impossible not to degrade an otherwise crisp apex. You make one 'good' pass, then follow with another pass that's got the angle tilted slightly off, and the crisp apex that was previously there will be rotated into one of the inserts on one side or the other. Yet another pass may tilt the blade a tiny bit the other way, doing essentially the same to the other side of the apex. The net result of all this is an apex that'll be somewhat rounded off (at least), or downright blunt.
The round rod-type ceramic inserts would be the least damaging, but they'll also be more prone to rounding and then burnishing or polishing the rounded (therefore blunt) apex. The crisp-edged carbide inserts are the absolute worst, because they'll grab and pinch the fine edge like a pair of dull scissors pinching and ripping a piece of paper; it does nasty things to the edge when that happens.
You can get crock-stick or Sharpmaker-style 'pocket' sharpeners that leave an open space between the base of the rods at the bottom of the 'V' arrangement; or at least, the rods are long enough that the edge doesn't have to bottom out. At least with these, you'll still essentially get the same ease of use and portability as with the conventional 'pull-through' sharpener, but the apex of the edge is less likely to be ground away against one side, while the held angle is a little bit acute on the other side (working only the shoulder of the bevel). Instead, the apex may just bottom out against the (usually) plastic base for the rods; that shouldn't damage it.
David
