[Coda]

Tennessee's law prohibits things that are designed to protect the knuckles when striking, like brass knuckles. Some security keychains are made around this design (the most popular is a "cat" keychain where you put your fingers through the eye holes and the ears are spikes) and would be illegal under that ordinance, but the Kubotan (especially non-spiked varieties) ought to be okay.

That said, one thing should be noted when it comes to any form of self-defense carry item: The entire point of having such a tool is not to actually defend yourself, because in general they rather suck at it. (The cat keychains are especially bad.) The point is that it gives you a way to make attackers think that you're not going to be an easy fight. They're still going to overpower you if it comes down to an actual fight, but unless they're hopped up on drugs or something the risk of getting hurt during the struggle is a pretty big deterrent. Your goal should be to show that you mean business and you won't take an assault passively, and then GTFO.