The book is so-so in terms of low carb variations. Its really no different than Atkins book except that you eat high carb on weekends. Its not revolutionary stuff, but maybe its a new concept to a lot of people. Personally, I think Bodyopus is a much better book that the Metabolic Diet, particularly in terms of health concerns while dieting. BO is also more entertaining.
The best keto book ever written is "The Ketogenic Diet" by Lyle McDonald. Its much more technical than most people are used to, or can probably comprehend without having done quite a bit of research into biochem, or even a college level human bio class. It has all the nuts and bolts and gives the real deal on keto diets.
The updated version is "The Ultimate Diet 2.0" which is much more reader friendly and has all the latest research on training, hormones, nutrition, etc. It would be my single recommendation for a diet book.