There isn't much to say about this book, because this book doesn't say much.
Actually, you could say it says half of what it should, since half of the book is not about the guidelines, but about how great guidelines are. Not that useless, but a simply "they are good, Mkay?" would suffice.
About the guidelines themselves, they are heavily based on Google guidelines, mostly because those guidelines and this book have the same author. There is no amazing things or suggestions, mostly of them are guidelines that everybody follows and others are mostly harmless in the sense that they don't affect reading, like double quotes instead of single quotes.
So, nothing really ground breaking, but not bad either.