I don't think it's a great weapon to use. It's not bad, but it raises certain problems over a baton or tonfa.
To effectively use it, like how you see Bruce Lee using it, you need to be able to perform movements where you wrap one baton over a shoulder, around the rib or under your armpit. Cops have a crap load of gear around their belts such that the baton would get jammed when trying to swing it under your arm or around your rib. You don't want to damage things on your belt, like the radio or have it get caught up on something while trying to defend yourself. And, just like other weapons, you need to practice with it to be proficient with it. A lot of cops don't practice baton strikes. But really, you don't need to. And that's one of the reasons police departments issue a telescoping or non-telescoping baton to their cops, using it is very simple and doesn't require constant practice.
The positive is that a smaller police officer, like a woman, can use the nunchaku to leverage more hitting strength because of its design.