The owners manual that comes with the 5D Mk II does little more than tell you about the buttons and menus. This book does so much more. It's better organized, and with nearly 500 pages of information, tells you why you should use each setting and control, while relating them directly to the most important dSLR concepts.
I love the logical format this book follows. The earlier chapters briefly introduce all the important features, so you can immediately begin using your camera, without bogging you down in details. For example, things like bracketing are explained with simple instructions for setting bracketing. If you want to know more, including why you should use bracketing to get the best exposure, or how to use bracketing to create HDR effects, the author refers you to the chapter that offers the additional detail. That's much less complicated than the manual that comes with the camera, which frequently uses multiple cross references that have you jumping all around to learn how to do something simple. With this book, it's "basics first" and "advanced concepts later," which makes it far superior to the hodge-podge that is the nearly useless manual that comes with the 5D Mk II.
I looked at a couple of the small pocket manuals also available for this camera. This book goes far beyond all of them in explaining why you'd want to make each setting, and how to use the features of the Canon 5D Mk II to improve your exposures and take better pictures. The large section on using Picture Styles came in very helpful. I did not find this much information on using custom Picture Styles in the Canon manual, nor in the other 5D Mk II guides I looked at.
The chapter that explained how to work with histograms, and explained how the 5D Mk II's autofocus system works was worth the price alone. In its 500 pages Busch spends about 95 pages just to explaining the nuances of the menu entries and what each option means. Nor does the manual that comes with the camera contain an exhaustive look at Canon lenses, their features, and descriptions of the cream of the crop.
If you want much more information and solid advice than you get in the manual that comes with the camera, this book should be your first choice.