Like with most of these kinds of technical books, you'll get more out of it if you're following along with the exercises -- either explicitly, or (maybe more so?) by applying the discussions to your own projects. Freeman does a good job of discussing React, but it's important to know that React's actual footprint is pretty small, and so most of the discussion is more accurately about:
• common patterns that show up in React applications
• pitfalls and anti-patterns to avoid
• companion packages (e.g., Redux, React Router)
• integrating with other common technologies (e.g., REST APIs, GraphQL)
Coverage of testing patterns seemed light to me, and I'd have liked to see the introduction to the topic earlier, and then sprinkled throughout -- but that is a personal nit-pick.
If you're already a competent developer with JavaScript, this book can help you get up and running with React and its surrounding ecosystem. Would recommend.