This was a great product, but I think students for the GRE need to recognize what it is for. It is meant for students who need extra review and practice on problems, more than what the comprehensive test books cover.
It does go into extensive detail about math you use on the exam. The first half covers the kinds of math (arithmetic, algebra, and geometry) and reviews those things we learned in high school, but may have forgotten. The second half covers the question types (comparison, word problems, and data analysis). There is a lot of material, so you have to skim through what you know and focus on your weaknesses.
I got this book after going through a comprehensive GRE test book and taking several practice tests. I was weak on the quantitative section, so I needed extra work, and this helped. My math score did improve dramatically after a week of intensive study with this book.
So, I recommend that you don't get this book when you start studying for the GRE. For people that are already strong in math, a regular GRE book might be enough. But if you practice and see that your math score is weak, use this one and study hard! It will definitely help.