If you convex your edge, they'll ruin your day.

But I have one similar to these in my ditch kit, I've used it on most of my knives. It even does well on a machete. It doesn't replace my good stones, but for emergencies it's fine. Five passes on the carbide and twenty on the ceramic will put an edge on a SAK that I can shave leg hair with. (If I test on my arms, I look like have mange or something.)