I used this clasp on a paracord loop for a flashlight while running. If I accidentally drop the flashlight, the magnet keeps a loop around my list, but if I drop my hand it detaches: just what I want.
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Pros
I like that you have to intentionally separate the two parts. No accidentally loosened keys.
Cons
Broke after about a month of use. The magnet has come out of the plastic case.