I am not a member of the A.A. However, I am a practicing Thelemite from a different branch of teachings. As such, I have a deep interest in all things Thelemic, and especially with documents and information relating to the A.A.
I would consider this book an essential reference to any Thelemic student, or anyone seriously interested in the systems of magick developed by Aleister Crowley. This book is crammed with useful and fascinating information. Further, the book is lucidly written, and the author is an obvious authority on Thelema. He makes clear whether he is making an assumption, or where evidence can be found to back up his statements. He also allows for differences of opinion and states his reasons for his own.
I'm giving the maximum rating just because of how much useful information there is. Having said that, this may not be the right book for a beginner or someone looking for a introduction to Thelema. This book would primarily benefit experienced Thelemites. There are multitudes of references to other books and writings, with which some comprehensive prior knowledge is immensely helpful. But there are also many gems to be found for the beginner as well.
If I had any problem with the book, it is a minor one. Which is that Eshelman is obviously biased towards favoring the approach of his own particular lineage. Sections that discuss the turbulent history of Thelemic orders tend to gloss over many vital details, often in favor of the Soror Estai lineage. Eshelman is looking at Thelema through an effective, though very particular lens. I also understand his attitude of following as precisely as possible Crowley's original intentions in order to preserve the effectiveness of the teachings. The reader should just keep in mind that this book is just one snapshot of a much wider community of Thelemic teachings and practices.