After I get my new printer up and running, I'll be doing Mysterymakers latest build, which uses the "screen used" mount pattern and hardware which I reeeeally like. It seems VERY secure. My current pack though... it would take a pretty good yank on it to pull it free. The bottom magnet helps a lot, but it's not foolproof... because we know how fools can be with costuming.
A friend had a "fool" at Dragoncon one year put that to the test, when they got punched from behind while wearing their USCM armor... which is metal like mine. The girl who punched him was holding her hand in pain because she thought it was plastic armor and it would be funny. Served her right. (^_^)