Are Nunchucks actually viable as weapons in a fight? All I have ever seen them used for outside of TMNT is very stylized...or people hitting themselves in the face or crotch.
Yes; they’re illegal in several states because of it. Like the tonfa and the sai, they’re a fantastic “fuck you” weapon against the samurai. Traditionally, they’re made from bamboo with rope, but modern ones come in metal and have a chain connecting them. They’re easily concealable too, and, you’re not trying to be fancy, it doesn’t take much training to be able to screw someone up with them. They’re a lot like a shorter version of the flail; you generate force through rotation and then connect to devastating effect. When they rebound off the victim, you can use that to kick start the inertia for the next strike. You can also duel wield them, but a single works just fine.
The key is learning the proper rotation of your own body as you turn them to use yours as a form of catch and release while the momentum builds and they are maneuvered into different positions. Commonly, one catches on the upper arms, shoulders, and ribs. Unless we’re talking about the old school comics, TMNT actually hides how dangerous they are, especially against unarmored opponents. The turtles originally killed people in the Mirage comics, which is why they have the weapons they do.
The nunchaku are a real weapon. But, because of the design, they’re very difficult to safely use in stage fighting. If you need a visual reference, Bruce Lee used them in several films.
It’s worth noting that, due to the danger nunchaku pose to other stuntmen, they’re something of a rarity on film. Bruce Lee’s phenomenal skill was the reason why he could use them in his movies and why he had the trust of his stuntmen not to hit/kill them, they were also occasionally made of plastic and probably padded. That said, Bruce Lee really is the best, so he’s worth watching. Just assume every hit involves a broken nose or jaw or wrist and there’s a lot more blood.