They work well enough. Smith makes one that is pretty decent. We used them at my restaurant because they were soooo much easier to teach people how to use correctly verses a stone. They use carbide cutters and you should use them judiciously or they will put a really funky bow in the edge of...
There were times I made way too much money for a uneducated redneck and spent it stupidly. Even then I would not have spent $400 plus for a pocket knife.
Quite a while back my granddaughter took this up for about a week. If memory serves I cut a 2x4 into 3” pieces and glued them together so that the end grain composed the face of the target. May have been several 2x4’s .