I like that it seems to work on things where other products don’t, but I’m not crazy about mystery ingredients, and the instructions to wash items thouroughly after cleaning them with it.
There isn’t one, really.
“Magic Eraser” type sponges are simply melamine foam. They work through abrasion.
The reason they tell you to wash things is because the sponges break down fairly quickly and you get bits of of them on things.
As far as I know there is no “ingrediant” or chemical in them. They supposedly work with abrasion. Like very, very fine sandpaper.
I think they tell you to wash items thoroughly afterwards to get and residue off them, like getting sawdust off of a board you just sanded.
Warning- they do take the shine and coating off of surfaces. While they did clean up my vinyl kitchen floor nicely they did take off it’s glossy surface so it now get’s dirty 10x as fast. I’m recoating it this weekend with a nu-floor type wax/polish/restorer.
I know guests can’t search, so here are a couple of recent related threads for your reading enjoyment:
http://boards.straightdope.com/sdmb/showthread.php?t=438509&highlight=melamine
http://boards.straightdope.com/sdmb/showthread.php?t=441250&highlight=melamine