I would recommend this to anyone who wants to save time and become efficient at working out.Good, but limited. This book discusses interval training and is a good starting point for anyone who is new to the concept. However it is basic, and unless you have no idea what is meant by "interval training" then you will not learn anything new. At its heart the message is, go really fast for a minute, then slow down for two minutes, repeat until done.
The most glaring problem is that the book only talks about interval training as manifested in the traditional cardio sports (running, swimming, cycling, etc.) It does not talk about ways to incorporate interval concepts into your strength training routines, and even worse does not adequately talk about how to incorporate your strength training with the interval program recommended.
I think this book is most useful for the type of people who "just run" (or just "whatever") at a steady pace for a predertmined time and have no plans to lift weights. However, if you are looking for a more holistic program that will cover more aspects of fitness, then I would suggest searching further.