That design may only help in situations with ideal conditions , where the victim cannot already swim faster and further? Seems like there wouldn't be enough stored power or speed for towing passengers far from Shore? If there's wind, waves, or currents, they might easily overpower towed victims because of underwater profile, which present a non hydrodynamic shape with a lot of drag while partially submerged? My vote is for gimmick.
Many years ago I purchased a WW2? Army Surplus fighter pilot over water ditch survival kit, stored in a box slightly larger than a shoe box, cost only a few dollars because the inflation canister was missing. It resembled a large oversized mummy sleeping bag when inflated. I had intended to use it for a remote hiking pack in raft, as there was nothing existing available that was as light, compact and durable at that time. Used for my trek into and deployed at Alpine Lakes and such. Didn't work as well as any of the modern pack-in rafts that weigh as little as 2.5 lb and occupy tiny space smaller than a loaf of bread.