Magic Eraser is a plastic that "crumbles" and becomes a 3000-frit abrasive. Which, curiously enough, is what Bon-Ami cleaner has always been. Diatomaceous earth, aka Fuller's earth, a fine abrasive that was also used in traditional "tooth powders" and then in tradtional "white" toothpastes like Crest and Colgate. All the same thing, all 300-grit abrasive. Comet, Ajax and other cleansers switched to the same mild abrasive back in the 90's after getting too many complaints of damaging plastics. Zud or Bartender's Friend use something similar, plus oxalic acid to clean rust--which should have no value to a diver.
There's simple physics behind it all, but there's nothing that an abrasive will do besides clean off dirt and oils, which MIGHT be "seeding" water drops to condense and fog the glass. Commercial water repellants really should be able to outperform them.
I'm from the "slosh a little water around" school. Never have to pack it, never have to apply it, never seem to run out of it. No warnings about keeping it out of my eyes, either.
