I assume you mean BIG water. In inland waters - maybe excluding very large lakes such as the Great Lakes - I don't need my PLB to float, so long as it is somehow secured.

Still, even in BIG water I'd rather have a non-floating PLB than no PLB at all.

You need it tethered regardless.

FWIW, I DO NOT consider a buoyant PLB a requirement for overwater or marine use. Even if it floats, it still needs to be tethered to you to prevent loss, so buoyancy gains you little, really. Moreover, in the case of the ResQFix, it means you can no longer operate the beacon one-handed. You have to partially remove the "float coat" in order to deploy the antenna. It's really a bit of half-baked design.