This is a short but very informative book that describes how the author has implemented and used Scrum and XP. Don't buy this book if you want to learn in detail the process behind Scrum or XP. Do buy this book if you understand the basics of agile and are looking for details of a real world Scrum and XP implementation that tells it as it is, 'warts n' all'.
This is a short book but that doesn't mean that it is lacking in value. There are lots of useful nuggets in it; though some may seem very obvious. Everything is obvious once you know about it ;-). There is also a very good example about determining and using your teams focus factor.
In summary, I recommend you buy this book!