Yep, it’s out.
In terms of functionality, it’s a single non-lethal melee item which you can throw and melee attack to knock someone out and, unlike a certain bottle, doesn’t break no matter how hard you hit it, and you don’t drop it when melee’ing, which a couple of other items do for some reason.
To unlock it you need to shoot 4 inflatable beach balls. Two are on the harbour beach, one is on the rocks next to the harbour starting location, and a fourth is in a corner of the balcony of the apartment neighbouring the safe house (under the parasol). There’s probably more, but those are the four I shot to unlock it.
In my opinion there should have been two boots instead of one, but whatever.