Use it all the time. Got tired of music when working out or walking and now listen to books on tape.
Not cheap; about $15 per month and you get 1 credit per month. Audible books run around $15 to $20 per book (some more, some less; most popular books last 9 - 12 hours listening; but tons of short ones and some really long ones.
They recently upgraded both their phone app and the website, so it is easier to track you reads.
Also recommend you check your local library. Many now have free audible books for library members. Won’t be cutting edge stuff or as good of a user experience, but will augment your Audible nicely.
Nothing better for a long car ride than a good book on tape.
So 1 credit is worth 1 book (any book available on Audible no matter what the price retail)?