This book was recommended to me by my Alexander technique Instructor. Although no book can really replace an Alexander instructor, this book is a very good companion guide with your lessons. The author gives a very good introduction to the technique, an understanding into what the technique is and what it is not. He also gives several examples and pictures to illustrate 'good use' and 'bad use'. There are many useful insights that illustrate how the technique is not about maintaining a certain body posture, but it is about the use of the self (The self includes body, speech and thinking). The author also beautifully explains the concepts of non-doing, end-gaining, inhibition and direction etc.
There are also accounts by people who caused injuries to themselves through bad use and recovered after learning the Alexander technique. These stories are pretty insightful and inspirational. I myself have suffered from chronic hip pain because of misuse, and have been on the path to recovery after learning the technique.
The technique although quite simple can take a considerable amount of time to learn, understand and implement into everyday use. So I would highly recommend this book (along with taking lessons from a personal instructor) which can accelerate one's understanding of the technique. I benefited a lot from reading this book and it helped me improve my use tremondously.