Velcro will hold it...but sucks to remove. I have had instances where chunks of drywall came off with the velcro. I still use velcro between devices and TVs but i prefer to screw mount devices to walls/cabinets.
The magnet thing sounds interesting. I have to check that out.
On a yacht project the boat yard used snaps to hold everything in place. Male side of the snap on the wall or shelf and the female side on the device/component. This worked really well. Just snap the device in place. You have to create a jig for mounting the snaps or you will never get them to line up.
Avid Stamp Collector - I really love 39 Cent Stamps