The book is great. the lessons are arranged in a way so you can start easy and then work your way up, while also being able to choose any lesson if you're an experienced bassist. The book provides explanations for the usage of the contents of every chapter. The book also comes with a good set of audio files that can be helpful when practising.
Something to keep in mind is that this book requires a bit of knowledge within musical theory (mainly around rhythm and if you're feeling fancy, chords).
There is, however, an issue in clarity. But since it's only from verbosity, it's not hard to deal with.
Overall the book provides you with more than enough lessons to keep you going for a while and always give you something new to learn.