I bought one of these
at the BIG gun show in Tulsa. I've seen the guy selling them there for, I dunno, more than a decade and I decided that if he was there, I'd buy one, so I did. I think they are actually cheaper on Teh Smilez. It does a great job on knives that aren't sharp, using the 300 grit diamonds. I bought an extra set of diamonds in 1000 grit. That works well for knives that are already fairly sharp. Then I touch them up slightly with one of these.
that I bought at Sturgis in '16. I bought a couple more to leave around. They are only $15 shipped, and they take paypal.