I do not recommend this book. The book brags about success stories. If at least one employee heard of OKRs, the author would claim the company's success solely to OKRs. This book takes survivorship bias to the extreme. What this book does not talk is how the mentioned companies, including OKR mother-ship Google, constantly fail. You might assume those teams didn't implement OKRs correctly. However the book does not tell you the correct way and you have to figure out it for yourself.
Without that, it's a pigeon superstition:
However I would recommend the resources at the end of the book.
Don't get me wrong, the topic of goal setting and uniting teams is very important. OKR is a fancy word for the goal setting and it creates more confusion. Without understanding of OKR implementation details it's too easy to fall into cargo culting.