I think you don't need to buy first book to understand second book if you already built a simple web application with this or similar stack.

Later this month I plan to somewhat re-write first book, many packages push changes often (Next.js and Material-UI) plus many explanations can be improved and I need to do better job with diagrams. First book, Builder Book, is either for junior developer or someone who wants to save time to learn this particular stack.

I hope this helps.