This is one more of those in-progress books that are so trendy nowadays among tech books. Instead of being published in Leanpub is self-published, but as many of them, it suffers from the same issue. It's not advancing and has got stuck. Most of the half of the book is still to complete, containing barely section titles, and the other half is not completed. The author has clearly stopped adding new content, and even, when he did it, it's impossible to follow what is new from what you already read. For this price, I really expected more dedication from the author. At the end, I had to go to the sources he said he used to write the book, as those are already available at 100%.
I don't recommend, at least, until it's 100% completed.