This book is HIGHLY anecdotal, and while it does seem to make use of some scientific journals, they are largely taken at face value i.e. not meta analysis and do not usually quote any actual data. Not convinved that this is about science, rather it is opinions about 'science'.
The truth is that there is very very little reliable data about the effectiveness of meditation and mindfulness. It's very difficult to separate the practice from lifestyle; we simply do not know enough about it. Meditation is NOT a science, and in my opinion, it shouldn't be treated as one.
Meditation CAN change you. So can books, and conversations, and experiences, and hair-dye. Sure, it's not a one size fits all; there are different kinds of meditation. Some poeple would even argue that running is a form of meditation.
If you're buying this book because you want to know if meditation might work for you, the best thing you can do is try it. If you're buying this book to confirm your belief that meditation is sensationalised nonsense, then why bother? Google confirmation bias, and instead go and do your own research. People should stop looking for opinions in other people's opinions and do their own research. What do YOU think? Does this work for YOU? Who cares what it means for someone else? You're NOT someone else!
Lastly, if you're buying this book because you're unhappy, and you think meditation might make you less unhappy, you're looking at it from the wrong perspective. The chances are, your unhapiness is a symptom of being human, and your problem with your unhapiness is a symptom of your society telling you over and over that being unhappy isn't normal, while literally making you work 5/6 days a week, taking your pensions away, and paying you less than a living wage. You don't have to fix it or change it. You might want to, but you have to set that aside. Look at your life and try to understand why you're unhappy. Meditation will give you the time, space and skills to look into yourself and attempt to understand your feelings. It won't necessarily change them, or you. It can, but you can't go into it expecting that it will -- zazen is good for nothing.
If you want to be happy, and you want other people to be happy, campaign for change. And don't waste your money on this dumb book.