The manufacturers of the $30 Shark Shocker say that their neoprene band full of stupid magnets would repel a shark attack. They say they have tested it in this video and it "works". Really?
That guy in the water is facing reef sharks, which are non-aggressive at all. I've been diving with reef sharks plenty of times and they get easily scared by humans. They will not attack you, so I don't know what this video proves. I'd suggest they drop Mr. Speedopants here near a white shark in South Africa. Or in the middle of a hammerheads pack. Or just get him to play poker with a bull shark. That I'd like to watch—or maybe not, because I'm sure that it would be one sad bloody show.