I should have clarified. The slicer ones have been working fine as long as you don't put thick knives in them. If you put thick knives in them, they will open up and become loose. I put a 5 inch old Wusthof in a slicer edge guard and it started to get loose.
The chef knife edge guards open up no matter what's in them; you're best off using these for thicker knives. I have a 10 inch (I believe) chef knife edge guard for a Forscher Scimitar. The knife barely stays in it and it's the only knife that i've ever put in it.