A measuring ruler with Florida species identification built in.
Saltwater regulations are species-specific, they change, and enforcement does not accept a good-faith guess. Slot limits on redfish and snook, closed seasons on grouper and snapper, and minimums that differ between Gulf and Atlantic waters are all things you are expected to know at the boat.
Having the ID and the ruler on the same tool means you settle both questions in seconds, before the fish has been out of the water long enough to matter.
Genuinely useful for anyone still learning a gag from a red grouper.