Which is critical not only as a matter of morals, but because it's illegal to intervene on the side of an aggressor. And there can be two stages of that, the first to threaten or use physical force, and the first to threaten or use lethal force. The definition of the latter is complicated, not to mention controversial and subject to second guessing etc., especially when the other person doesn't have a weapon.
The general advice is don't, or as Massad Ayoob puts it, if you were in a hospital and saw a random person needing low 6 figures of medical care, would you give him a check for it? Because that's what it takes to adequately defend yourself against a serious criminal charge.
Which includes intervening, in many ways, where there is no aggressor (as then you become the aggressor, not merely someone intervening on the side of the aggressor) -- a possibility which it is quite likely that the would-be vigilantes who would have the greatest inclination to sign-on to such a system are likely to not consider when responding to a call.
1. Creep wants to hurt vulnerable people. 2. Creep buys this system. 3. Creep waits for vulnerable people to be in trouble. 4. Creep shows up on the scene and collaborates with the attacker(s).
This is begging for disaster.
I've personally witnessed the ugly mess of an overzealous rescue, a rescuer labeled assailant when the victim changes their mind or late responders are simply confused and of course violent wisdom of gathering mobs.
Digitally amplifying a scream this way is serious business. Assault and attacker, words the site uses freely, are dead serious yet being applied to an easily activated 'bunny' pin with implied 'rewards'.
I hope these folks think heavily about the potential implications - not just intent of what they're doing here.