As I understand one of the ways of using Kubotan is wrapping it with your fingers, wrapping it like a fist. If you use your fist while holding the Kubotan, do you endanger your hand and fingers? On impact, can the Kubotan fall down or move? Is a regular fist more effective than a fist holding Kubotan?
I talked about these kinds of things and briefly referred to kubotan keychains in my answer below:
That question specifically asked about using a carabiner. I also talked about brass knuckles.
My overall opinion of these kinds of self-defense weapons is that they're nearly useless and often do either injure your hand or give you an unrealistic expectation of their effectiveness.
Kubotan keychains are light weight and portable. You can put them in your pocket and carry them with your keys. That's why people like them. You'll always have it on you, so the theory goes.
The problem is that if you're going to have a weapon, it better be effective. Part of that effectiveness comes from knowing how to use it properly. Part of it comes from the weapon design itself. The fact that the kubotan is so light in weight means that it's also not going to add significant power to your punch, if that's what you want to do with it. Some people use a roll of quarters, and actually that's more weighty than a kubotan.
But as I mentioned in my previous answer, you don't want it to be weighty and to use it like a roll of quarters. Using it in your punch will merely increase the chance of you breaking a finger. So you wouldn't use it that way.
Kubotans are supposed to be used in a thrusting or stabbing motion. You want to hit the other person with the pointy end. But think about that. How effective is that going to be vs. just punching someone? Not very. Yes, it concentrates force in a small area. That can hurt. The most damage it might do is to break a rib, but that is pretty unlikely. It's definitely not going to end the fight.
Another way kubotans are taught to be used is in grappling. You can press against someone's wrist with it while using it for leverage, and it works like a pain compliance technique to release your opponent's grip. But once again, how effective is that going to be vs. knowing how to grapple? If you're spending time trying to position it just right, and you're using two hands to release someone's grip, then you're opening yourself up for being attacked.
My advice: Keep it in your pocket. Take it out only as a last resort when you're wrestling with someone and he has you in a lock you can't get out of.
A small pocket knife will always be much more effective. Granted there are laws against those in many countries and cities. In the U.S., it depends on the state, but generally pocket knives a few inches long are legal to carry. You can still lose in court by using a knife in self-defense, because even if it's legal, there is a bias against people who use knives. The general public perceives knife violence as being something only "thugs" do. But perhaps it's better to lose in court than to die or get seriously injured in a fight.
The question also asks how easy is it to lose the kubotan during the fight? I guess the worry is that your opponent will pick it up and use it against you. Personally, I wouldn't worry about it. It's unlikely they will know how to use it against you. They probably will try to use it to make their punch stronger, but as I said, it's useless for that purpose. Just don't take it out unless it's a last resort.
Remember when I said that the effectiveness of a weapon depends on you knowing how to use it? That means you need to train to use it, and train often. It also means that part of your training will be against someone armed with a kubotan in case they get a hold of yours.
It seems entirely realistic that if you do take out and use your kubotan during a fight, you will want to get rid of it at some point. It's only useful in niche situations (like the grappling one I mentioned). You will not want to use it for the entire fight. You'll have things you want to do that will only be hindered if you have anything in your hands. So you're going to want to discard that kubotan at some point. Maybe you'll throw it at your opponent, or you'll toss it to the side. By the way, if it does have your keys on it, too bad. You just lost your keys! Bad idea to put your keys on a self-defense weapon, no matter how enticing the marketing pitch is.
Hope that helps.
A kubotan can be hugely effective, but punching with it in the manner of a roll of quarters is not recommended because you're likely to hurt your hand.
Kubotans are effective because of physics—puts all the force into a small surface area capable of delivering a definitive strike.
The best method to use a kubotan practically is to use a backhanded grip, a form of hammer fist.
Here, you're not generally hammering down, but in a horizontal manner. The main targets are the kidneys, the throat, the solar plexus, and the temples, but any strike anywhere on the body in the manner will be painful, and certainly give you a moment of advantage for followup strikes.
- The caveat here is that it's a close-range weapon, so if you don't have the defensive skills and footwork to get inside and stay balanced, you're unlikely to be able to wield it effectively.
(Another advantage to kubotan is it carries less potential legal liability than a knife if you seriously injure or kill your opponent, and, typically, you don't want the blood of the type of person who attacks people in the street getting on you, especially if you get cut.)
If you have sufficient training in any martial art from a good instructor, and are worried about defending against a bigger, stronger, or more skilled opponent, kubotan is a great street weapon b/c it fits in your pocket.
- There are also versions that include two blunt finger spikes, and those do facilitate punching b/c all the force is concentrated in the spikes.
Doesn't protect your fist in the manner of brass knuckles, but concentrates force in a smaller area, reducing impact to the knuckles. These types of kubotans also allows the hammer fist in addition to the punch, without changing grip.
A skilled practitioner can also use it for a thrusting strike from the top of the fist, such as under the chin where the glands are, or into the ears or temple, but it's more difficult and so not recommended as the go-to.
Never underestimate the utility of blunt-force trauma.
From my expertise derived from watching the kubotan-related "Hard to Hurt" channel's videos on YouTube, not very effective. Yes, conceivably you could hit an exact point with it and do some damage. Much more likely, you and the bad guy will be flailing and grappling, and you'll be adrenalized and losing your fine motor skills, and you won't have a chance to.
As Mike says in those videos, if you don't know how to move and protect your head and strike with no kubotan, what makes you think that you're going to be able to thrust or hammer or punch with one in your hand? If you're not already trained up in joint locks, what makes you think that you'll be able to use it to do a joint lock with it?
Besides which, small kubotons with no "finger depressions" and no "stop" on either end will slide through your hand.