Yes, this is Cypraea caputserpentis, no, they don't have specialized radular teeth like cone snails, no they aren't dangerous, yes, they do scrape algae and microorganisms off the rocks and glass. They don't ever get any larger after they form teeth, they just thicken the shell and stay the same size. This is a rough-water species though, and spends a lot of time out of the water, particularly at night. I wonder how it's doing in your tank?
Cheers,
Don