Once again, marketing clouds the waters, or stones. Ray Mears sells a set of stones with his name on it. They won't sharpen knives or impart some superior bushcraft ability on your knife any better than other tried systems.

Now, of greater import and not thought about: Never loan your best knife or let it leave your side. I have a Kauhavalainan puukko.It's my pet knife.
A few years back, I folishly set it down long enough for a idiot with some new wonder sharpening tool to grab it and demonstrate. He was convinced all knives were inherently dull, like somebody with a new religion. He ran his thumb disdainfully on the edge. The slice required; microsurgery, 5 stitches and antibiotics. HE STILL ran my poor knife through this pocket grinder and wrecked an edge time and use had lovingly set, before going to the emergency room.