I used one of these pocket sharpeners for about 5 years, and I can tell you, if you put enough lateral pressure on the handle, you can tear off quite a bit of metal with each pass, more than enough to reshape the edge. You can also put a pretty sharp edge on a blade once you learn the touch. It will knock bent edges back to true just like a good butcher's steel, which is probably the best feature about the thing.

I used to cut a lot of cable with my old Leatherman and occasionally I would roll or dent an edge. Using this little tool I could bring the burr back up to plumb without removing anymore metal, if I was careful about it. If the edge got too ratted out, I could tear it off and get rid of all the bigger jagged areas. It will leave the edge a bit ragged, but for a lot of field cutting I think that is actually preferable.

It was worth the pittance I paid for it, and it lasted long enough that I finally lost it. The square edges never took a dent or a nick, and never rusted.

It may not be the ideal sharpener, but as a field expedient, I can't imagine anything serving a better purpose.