So I read a couple of chapters that interested me in this book and all in all it is a very good introduction to Debian. The problem I see for me personally is that most of the information provided is, let’s say, “not up to date”. I’m sure that most of the stuff in there works right now on the newest Debian, but some stuff in the book is not only old but is getting on the edge of being deprecated or at least it is becoming a bad practice to still use this old stuff, nowadays. So the problem with that is, if someone seriously wants to start using Debian very efficiently and well, by putting time and effort into the book, then by the time they master the content and actually could pass a test for this book’s information, the information itself is already so stale, you basically need to update a lot of your information.
Therefore, as mentioned, all in all this book is a good introduction, but this will remain only as a starting point, if you really want to know current Debian.