Parts of this book are helpful is a primer to what has changed between earlier versions of Drupal and Drupal 8. In general, though, a lot of examples are lifted directly from Drupal's official documentation, especially early in the book. It feels like it has undergone to copy-editing as it is riddled with typos throughout. Worse, it has a lot of buggy code in the examples. I shouldn't have to spend time de-bugging the author's code as I'm reading the book. This isn't a Drupal resource that I can recommend.