I think knucks are better suited for someone that can successfully throw and land a cross or overhand punch consistently. For someone that is not skilled in physical combat they are better off with a pepper/oc/vanilla / spray/ gel.I think a lot of people are underestimating that concentrated pressure point aspect you get with knuckles.
You don't have to hit them in the head and you probably don't want to, very likely it'll kill someone in one shot. A good rib hit or even in the shoulder(!) and I promise you they will back off. If from nothing else then surprise, cause they aren't expecting it to feel like that...
I could hand my 11yr old daughter brass knuckles and she could hurt you.