This one of the first books I read during my exiting process (1996-1997).I find it very dark, and describing the worse of the worst - with no empathy (or very little) for the victims. Its is very much technical - maybe too much. It is very crude in the description of the various mechanisms at work in cults.
There is no part in this book for psychological analysis on the victims' side - leaves you with a very bad taste in the mouth.
Of course the author is an expert in this field. I'd say this book describes very well one side of the problem - which has several other sides IMO.
It's author was harrassed and attacked in every possible way by scientologists - very much like what's been done to John Mac.