I am writing this review for the benefit of people who are interested in this book for professional/educational purposes, or for personal interest, rather than the prurient reader looking for a good read about a sensational phenomenon.
To such an audience, I would say as an overview, the book is good. It is broad in scope, ranging from diagnostic indicators, treatment approaches, what to expect in therapy, the functions of dissociation, and self-help/coping strategies.
On the downside, its literal engagement with notions such as "alters" strikes me as slightly dubious. A lot of what is in this book is not what you would describe as "evidence-based" either. It's an interesting enough and informative read, but it lacks theoretical and empirical rigour. Part of the reason for this might be that the book seeks to be all things to all people - it is aimed simultaneously at "clients, therapists, family and friends", so that might give you an idea of the kind of level we are talking about. Also, because it is quite broad in scope, it is somewhat limited in terms of depth of coverage.
The "Choosing a Therapist" section is clearly aimed for people in the US of A, so perhaps not that useful if you're in the UK. Some of the discussions of therapy are rather "American" in content as well, so might not fit so well into a British therapy culture.
Hope this is helpful.