I would worry about splash back onto the "gun" itself. Like toilet brushes, I don't think I trust other people to keep the cleaning thing itself clean.
No it's if it can drop into the toilet bowl and siphon water from there into the freshwater supply. There's a rule for not fitting handheld showers where they can drop into the loo but people forget when retrofitting bum guns.
I would worry about splash back onto the "gun" itself. Like toilet brushes, I don't think I trust other people to keep the cleaning thing itself clean.