Probably as worthless as deer whistles for cars.
I can remember about 25 years ago scuba divers and snorkelers they had pods attached to their flippers to ward of sharks.
It didn't work then as advertised. The shark pods went out of vogue.
Maybe today there has been some improvement ?
Would you like to try these new version pods out down the Cape this summer?
There should be no shortage of white sharks to test the pods on. - Tom