Other reviewers have hinted at it, and I'll go ahead and state it explicitly: this book is overkill. This isn't necessarily a bad thing, though. The book provides a very detailed review of the math on the test, and the practice tests are far more difficult and involved than the actual test.
If you're looking for a good score on the Math Level 2 Subject Test, you don't need this book. The review is too detailed and the tests are too demanding. If you're looking for an 800, though, this is exactly the book you'll want. It prepares you for the one or two questions on the test that most test-takers won't even attempt, the one or two questions that could be the difference between a 790 and an 800. You'll cover things, like the latus rectum of a hyperbola, that probably won't show up on the test, but you'll be ready if they do.
The real strength of this book is in its solutions. It provides detailed solutions to each example problem and each problem on the practice tests. I found it very helpful to read through these solutions for every problem, even those I got right. In several cases, I found that the authors used a faster and more efficient technique. The book really emphasizes these techniques as a way to increase both speed and accuracy. In particular, it places heavy emphasis on leveraging the graphing calculator to solve problems.
I've come to expect that a test prep book will give a basic review of material, some generic "tips" (make educated guesses, use the process of elimination, etc.), and provide a couple of practice tests. This book goes far beyond that with a detailed and comprehensive review, clever techniques and methods that are actually helpful, and six challenging (but in the style of the subject test) practice tests with detailed solutions.
If you want the 800 and you're willing to put in the effort, this book is the way to go.