Ya, zero risk to everything once you get 7 or 8 police wielding them at the same time, per one violent person, in a crowded subway with potentially no walls to pin them down to, with the extreme possibility of someone just pulling a gun on you when you have both your hands occupied with a stick. Mancatchers work great on gifs and videos, but suck in the actual world. Especially when you get charged by a dude wielding a knife. You'll 100% have the time to "break the glass in an emergency" and to deal with said person. Especially when the situation turns from "let's run after this guy that skipped the fare" into "holy shit that's a knife and I'm going to die".