I often listen to those Nike Run Club couching sessions and there is often a guy talking through the session, and I can clearly hear what he says, so they should be fine with audio books too.

One thing to consider though is the amount of noise or traffic where you run. I normally run through fields, so it’s very quite, but indeed when I need to go through a couple of noise roads I need to volume up quite a bit to distinctively understand what he says

I’m using an older model from Shokz https://shokz.com/ It seems that now they sell newer models and different sizes, but mine would compre to the “openrun” model I guess.

I prefer them to the AirPods Pro (with transparency mode) or other in-ear when I run. Of course, as mentioned in other comments, the music quality is not what you are looking for here…

I like them because they are very stable, they allow you to hear everything around, and there is never that weird deep sound that sometimes you have with in-ear when you walk, which I really hate.

I use a bone transmission headset when I go jogging, they are perfect. I don’t need high quality music, just a background to keep me pumped and entertained, and I can perfectly hear cars, bicycles, and other people passing next to me and stay safe…