Well, the yoyo was originally created as a weapon, of course. Steel, or metal, and sometimes with bladed edges. Yoyo's can be pretty deadly if you think about it. Fine piano wire string, weighted down, swung at high speeds and can be hidden in plain sight.
It can also wrap around and attack from all sides of a wall/pole/or weapon.
When I saw the guy using it, while I had no interest in him personally, I did want to see how he used the weapons. I am always up for watching some Yoyo-fu.