Hmm, magnets - sounds interesting. What worries me is a strobe coming loose so that it's hanging by the cable alone. I usually clip them to a bit of cave line as well so they can't fall too far.
I have started using bungee straps placed on the tank in advance. For sidemount this means the diver can reach down and adjust the strobe from the top of the tank to the side as they pass through different areas. For backmounts it makes it a bit easier to mount the strobe in there while underwater. If you have enough strobes mounting one on each tank makes for great lighting behind the diver. A single strobe between backmounts (up the top) can work well for lighting, especially if it's angled slightly up and you instruct the diver to stick to the floor and keep their legs straight out behind for photos. Or place it right at the bottom between the boots to light the passage behind rather than overhead.
I was previously using duct tape for strobe mounting, added before the dive which sticks well when the tanks are dry but obviously isn't adjustable. I have also seen people taping/clamping strobe arms to tanks and then being able to adjust the strobe on the ball as they go.