I been stopped by cops a few times and never had an issue with it, when I stopped I keep hands visible and inform them. As a matter of fact I haven't even had them ask me to remove myself or firearm from the vehicle.
To answer falling off on a bumping road, no, not even shifted and I drive down alot of "rig board" roads for work to different locations. Those go-magnets are amazing and coated so it does not affect the finish of the firearm.
To answer placement I chose there, as opposed to under the steering wheel, one according to a couple of my leo buddies said it's smarter for being stopped if it is more visible. The biggest reason is entering and exiting the vehicle my leg hits it too much, does not knock off just annoying.
I mounted it closer to center console so it was not rubbing but had enough room to slide my hand down quick enough for a draw. I have always drove with a conceal in center console until I had a tax leach attempt to rob me at a red light. My quickest draw item was a screw driver sitting in console at the time. With this in worse case I can draw while leaning and start sending rounds down range while attempting to lean into better cover. If I had not had a screw driver in cup holder of console, and been trying to get into console I could have easily been hit a couple times before I reached my firearm.
Everyone has their preference, this is mine and the reasoning. I also keep an extra clip in my molly webbing of sun visor and in the webbing attached to the top of my center console as well.