Not always great. A good rule of thumb: could you easily hear someone talking next to you at a normal speaking volume? If so, you'll be able to hear with the headphones just fine. If not, you probably won't.
My Aftershokz are good for spoken word in noisy/trafficy environments unless I'm inside a car at freeway speeds, or operating a lawn mower. They could work in a car if they got a little louder.
Just be aware that they make it practical to tell that something is happening around you, but with spoken word you'll usually have to pause to tell what is happening around you. I.e., I can't understand what someone is saying to me if a narrator is already speaking into my ear.
