This book is very good, and absolutely recommandable.
The book is not very big (~100 pages) and can be read quite fast. It's also an easy read, as the language in the book is not hard as some other technical books might be. The explanations are good, and easy to understand, as well as the reasoning.
I enjoyed this book, and it's a great reference. It's size also allows you to read it again (And that's a great idea - Helps you to remember) to get the most out of the book.
The author knows what he talks about, and his advice really makes sense. You might already be aware of some of the concepts, such as filtering input etc, but Chris explains really well the ideas behind such concepts, and gives great examples of what can go wrong if you fail to follow the simple principles given.
All in all, this is a great book that really helps you, by teaching you best practices from a very experienced web-developer.
And the book is really great as a reference.