The rubber foam grips really well on my parquet floor, and the device looks really nice, traditionally stylish, and well made.
Not sure about the magnet, though. It doesn't seems strong enough to do much - but it won't work for me either way, as my carbon fiber endpin has a stainless tip, which of course means it's non-magnetic.
My only issue with it is that the magnet sits too high up, and can be reached by the tip. I think it would be nice to have a version with just an ebony "pit" and no magnet.