[Note: the version reviewed herein is the Kindle Ebook edition]
It probably should have been called "Mercurial: Moderate Overview and Author's Favorite Extension". A significant amount of the book is spent on MQ, the patch management extension for Mercurial. Since I'm not using hg to manage a set of patches against upstream opensource projects, this wasn't very interesting to me. I would very much have liked more time spent on other extensions, and more in-depth examination of various workflows that one can use with mercurial.
This book is also getting a bit stale, as mercurial like many fast-moving opensource projects has continued to accumulate new features and extensions.
Technically this book is opensource, and available on bitbucket. I couldn't get it to build, though.