I have had this book for a couple of years, and still dip into it from time to time. I found it quite easy to understand.
Although there is some medical terminology, it usually uses words as dancers would understand them - such as extension, which means a different thing to dancers and doctors. It tells you about how your muscles work and has a section on the spine, the hips and pelvis, factors deterimining turnout - physical limitations and how your thighs work, use of the ribcage, how the knee works and of course, the foot. It also has an excellent section at the back entitled "what we say and what we mean" - which was helpful in translating corrections given by the teacher, such as pull up and use your feet.
All in all it is an excellent book, there is not too much detail but it gives you basically what you need to know. I would recommend it to dancers and teachers both, and as it is separated into separate sections, you can go to what part of the body you are interested in first. It is a technical and anatomical book, but I found it very interesting and useful.