but carrying it in public is. Technically, it would be a weapon (blade length over 4") and it would be concealed.
Not that getting a concealed weapons permit in Florida is hard. You can get a concealed firearm permit in (iirc) a 45 minute class. I can't imagine a concealed weapon's permit to be any harder than that.
The bad news of Oz's weapons ban is for martial arts performing Tamigiri (test cutting). Live samuri blades aren't cheap to begin with (minimum $200 us, with prices climbing fast into the thousands for custom blades). Now those people are going to have to get permits, etc. just to keep their blades.