Not only did this book help me understand Deceivers, it helped me understand Excrucians in general -- how they break through into reality, how they can be formed from the core of a human being, why they do what they do, and so on. That alone was worth the price of the book. But of course the meat of this supplement is the Deceivers themselves, and we get a WEALTH of information about them, particularly rules for building them from the ground up (with a clear and complete example), starting with an avatar/lifepath and ending with the actual attributes, bonds, etc. In theory, you could use this to play a Deceiver PC (and there are rules for that!) but in practice, this will help me (as GM) flesh out my Deceivers (and, to some degree, other Excrucians) and make each one a fully-developed character.
A strong recommendation for GMs, entirely optional for players (who may appreciate the general insight into Persona and be inspired by some of the concepts, which could equally apply to Nobles).
[5 of 5 Stars!]