For the most part, the book is easy driving in the Audible version. It tells of his life growing up and a little bit of his time in the Great War. It ends with his experiences as a teacher of philosophy. Only those experiences that apply to his conversion are included. At times, he goes into a logical deconstruction of how those experiences were internalized and analyzed to produce his world view. When he tells stories from his life, the jeep is running across solid ground. When he dips into philosophy, you've got to get out and push the thing.
For that reason, you need both species of his work. I listened to chapters 13 and 14 yesterday while driving in the car, but had to come home and read them last night to really understand what he was saying. I'm still not completely there, but I'm close. I'd read the book about 6 months ago and had the same problem in reverse. The stories from his life left me unprepared for the hard slogging of the philosophical parts.
I'm going through St. Augustine's The City of God right now on audio only and it's much the same. While he's refuting pagan critics following the sack of Rome, it's easy driving. As soon as he gets into theology, you're pretty much done and have to find a solid copy of the book so you can get out and push.
Despite the need to flip back and forth from time to time, and the need to buy two copies of these kinds of books, I'm finding this an excellent way to muddle through philosophy and theology. The Audible version keeps you interested enough to want to push your jeep through the mud in the deeper parts.