Magflots are good for glass I bought an arculic safe one and it still scratched a little and no there was no sand in it. My lfs has one called hammer and there is a pirahn not sure the company that makes them.
If money is no object, Tunze or Magnavore. Tunze is available on this site, but I think Magnavores may be better. The Tunze ones are imported, which may account for part of the cost.
ive got a magfloat but i took it out and put a little tiny "twister" in there.
it doesnt float but its small and really skinny to get those hard to reach places the blunt mag could not.