Something I think is worth considering is in regards to an article I read that my brother sent me a while back.
Choosing a knife to carry
the point is you might be all ready to go and have your awesome tactical survival weapons from hell and any attacker is going down...but yeah you get in the situation and your @$$ is in jail for murder. I think something to keep in mind is your weapon of choice needs to be practical and something that you could justify having in a court of law. The article I posted recommends staying away from anything that is auto open, or is called "tactical" if it's a blade. a knife should be a utility weapon that you applied to self defense...
I think the same goes for anything you are considering using, brass knuckles, taser, shuriken, spikes, collapsible baton, kubotan etc. Can you defend in a court of law why you where carrying it? convince a judge and your peers that you needed to have it on you for self defense? and that you used it as a last resort? That you where not looking for trouble?
self defense is about being the one to walk away when S*#t goes down. It doesn't mean being battle ready for a gang fight. IMO
Just some food for thought...