What is a Persuader (also called a Kubotan)?

A 5 1/2" long cylinder made of plastic or metal which you attach your keys to. It can be used for pressure point manipulation, locks, or striking. It has a flat end with no points.

Is it legal?

It is legal virtually everywhere, EXCEPT in carry-on's on some airplanes. In some venues it is considered a martial arts weapon.

Where can I buy a Persuader?

They can be purchased from some hardware and firearms stores, mail-order, Online, or at a class.