Well worth getting this book for its useful tips and background information on the routes. I haven't dared to try the Game Tools yet, so I don't know how good the book is on this subject.
However, just like TrainSim itself, I'm afraid the book does contain some errors, which can cause confusion, especially on the Marias Pass chapter. It mixed up east and west at one point, and also refers to the wrong goods yard elsewhere, for example. Station stops in the simulator do not always match those in the descriptions.
However, all in all, the book is useful and interesing, even if it is written in American!