I was thinking freediving as it requires less energy than flippers though I’m not sure the decreased maneuverability of having the thing attached to you would detract from what you are wanting to do when freediving. The article does say you can dive with it, though the devil is in the details eg how easy is it to turn around? I suspice it’s not nearly as easy as flippers

Another interesting use case would be just tossing one of these into a boat that you own, or a kayak or whatever. Basically extra insurance to get you back in case your motor dies or you get swept out, similar use case as the surfboard