It would have to disable all the safeties. I don't see that happening. there are some possible issues.
1. I am not sure, but it may affect things if you try to fire it with it attached to the magnet. So having it under a desk, pointing and ready to just pull the trigger might not be a good idea. There would also be no place for the recoil to go.
2. Using it as a car mount when driving. I doubt the magnet is strong enough to hold the weapon secure in case of an accident. So if something did happen, your weapon would be rolling around your car like a hammer. If you want to pistol whip yourself, go ahead and give it a try. Even worse would be if the trigger snagged something. (unlikely, but possible) If you are going to permanently mount something to your car, may as well make it a holster in a good location. (The original question was about desks, but their video showed many car mounts and wanted to throw this out for people researching gun magnets. Sorry if it is a little off topic)
3. If the magnet is strong enough to magnetize the bullets, the bullets will probably bend and hit the guy in his belt buckle, cell phone, flask, pocket knife, or any other metal things and render the shots mostly worthless.
ok, i wanted a 3rd item and couldn't think of one, so I decided to amuse myself..... :rofl: and it worked
*** I googled gun magnet and found this, this design is what i am basing my observations on. I also watched their video at the bottom.
http://quickdrawgunmagnets.com/