I thought someone(s) here posted something not too long ago about why the magnets are bad, or at least not ideal. I was curious about them too.
As an alternate, as much grief as the Blackhawk systems take, this might be one place where they're an option, as they have that multi-mount modular system that lets them be secured to various surfaces (vehicle, under desk, etc.). Or maybe someone else makes a similar product that has better features?