I teach meditation and I am educated in biology, biochemistry and psychology. I am also a student of world religions and a yoga practioner. During my graduate school years, I was also a Teaching Fellow in Physiology and I teach workshops on pranayama and biofeedback. Therefore, I think my opinion has some weight in this arena although I realize there are more serious yoga practioners who have more in-depth knowledge than me. My purpose in sharing this information is to provide context from my review. I hope this is useful.
This book is incredibly detailed and goes deeply into respiratory physiology, muscles, practices and the details of pranayama practice. There are clear explanations, however, many people may find them to technical without a biology background or the desire to take this information in slowly.
There are many good diagrams and photos in the book that any practitioner will find helpful. In some cases, they are unique in the yoga literature in some way and I can't imagine not having this book on your shelf if you are serious about the practice of pranayama.
While this is not the most colorful or modern looking text, it certainly packs a lot of information into a small space. It is also written by someone who has travelled this road and understands it both technically and from the inside. In short, it is an authoratative text on this subject.
A lighter book along the same lines which I have also read is the Science of Breath. For beginners, this title might be more appropriate. However, any practioner at any level will eventually want to own this book.