I hesitated for months before buying this book. You shouldn't.
You should know that this is not a training manual or a tactics book. Its goal is to identify where your game is weak. If you are not already a Grandmaster, then it's certain that some areas of your game are weak. But which, and how weak are they? If club players, amateurs, even experts can focus their training on their weak spots, they will improve much more rapidly than if they get better in some area where they are already strong.
This book does a fantastic job of analyzing your game. Here is my experience. I don't get to play much in tournaments; my rating is in the high 1600's but my last major tournament I had a performance rating of 1820, and in club play that's about how I am doing. What should I work on to go farther?
I have done the first 40 problems in this book and scored them. Each has been given to a lot of players with a wide variety of ratings. By averaging how I performed on each of the problems, the author has assigned me an overall rating and a "rating" for how strong or weak I am in each of a dozen aspects of chess.
First, the overall estimate of my playing strength is right around 1800 -- consistent with my US Open performance and club play. But the breakdown -- wow! I rate a pathetic 1000 on pure calculating ability, and not much better on sacrifices. By contrast, the book rates me at 2400 on standard positions (like how to win a Bishop ending with only one pawn), reflecting the work I've done on such positions, and grasp of strategy and defense are both almost as high.
Interestingly, it rates my openings as the strongest phase of the game and endings as the weakest. Until the last US Open I thought the reverse was true, but in that tournament I consistently got strong middlegame positions against players rated up to 2100, only to collapse in the ending. The book accurately captures this relative weakness.
So my new training strategy is clear, and I bet it will work. For the next several months, I will be focusing on complex endings and doing intense practice in calculating them out to completion. That should address both of my weakest areas in one shot.
As part of my profession I have extensive training in developing tests to measure aspects of mental functioning. I am very impressed with this book, and would consider it a remarkable achievement for a psychology graduate student's dissertation.