For its price, I found this little booklet not helpful. The first 5 pages are essentially advertising for a consulting firm (the author's employer) that prepares pilots for airline interviews. The final 5 pages again are mostly advertising for that same company's products. A 14-page appendix contains a review of how to add, subtract, multiply, and divide (at the level of teaching you that 3 + 4 = 7). Another 10-page appendix contains addition, subtraction, multiplication and division tables. In the remainder of the book (55 - very small - pages), I found exactly one useful rule: how to meet a crossing restriction. There are one or two other rules that in years of corporate flying I have never found useful (such as how to calculate your hydroplaning speed - interesting in concept, but practically not very useful).
If your math is below high school level, this book may be useful to you. Otherwise, I wouldn't recommend this book.
If you are planning to prepare for an interview, I would recommend you save the money you would have spent on this book and buy "Everything explained for the professional pilot" instead; and if you are interviewing for a job in a turbine-powered aircraft, "The turbine pilot's flight manual" - both those books are MUCH more helpful.