Not good for fins in the California ocean. Rocks and sand get in the fins and the leash makes impossible to clear.
When used with fins in ocean the string gets wound up and too short to put the fin back on my foot in unstable water. My toes get caught in the string then I get pounded by the next wave. It’s dangerous. What would help is either a longer string or better yet, a swivel so the string doesn’t wind itself into a knot.