This book is a treasure. It was amazingly informative and useful to me, a solo web developer interested in learning more about typography for use in my own websites.
My appreciation and understanding of typography on the web improved after reading even just the first few chapters. Now, when I visit web pages, I notice little details about the typography that I hadn't before--the text size, the line heights, the approximate number of characters per line... the typographic color of the paragraphs... the design choices made with respect to text alignment... and, when I inspect CSS using Inspect, I can easily understand just about everything font-related, especially what each of the typical units (rem, em, px) really mean, and a bit about their historical contexts.
Perhaps most important is that this book improved my taste. I now understand that simplicity and readability are more important than big, eye-catching text. And, looking at my favorite websites, I realize that their designers understood this principle, as well.
If you are web developer or designer who wants an experienced, pleasant, and intelligent guide to usher you into the world of web typography, I cannot recommend this book highly enough.