My experience mirrors that of the other posters here. I've never had the clip move or get loose on me, and it is a nice inconspicuous clip that gathers no unwanted attention.
The only problem I ever had with a Mnandi clip was my fault. I flopped down into a chair and it snagged on a pronounced cushion seam. I put my whole body weight on it as I was sitting down (obviously), and it torqued the clip out to approx. a 45 degree angle away from the knife. However, I just took it off and gently bent it back and it was as good as new -- no looseness, subsequent play, weakening, etc. I was just glad I didn't lose the Mnandi!
- Mark