I have it and recommend it. It's very much the missing manual of FSX, and useful not just for the beginner, but also veterans who maybe don't think they have a full grasp of all the sim offers. For fully exploring instrument and radio navigation, its a must !
A criticism I've read in reviews is that the illustrations are all in black and white, and sometimes a little small. However, if you are reading about how to fly the Cessna 172 for instance, you will have the cockpit up in glorious colour on your monitor, and the book's black and white pictures are perfectly adequate as a guide for what to look for on the screen.
It sorely needs a glossary, as it can be a bit difficult to keep track of terms, acronyms and abbreviations ( well, at my age it is! ), but thats really my only gripe.
A very good book, and if I lost it, I'd certainly buy another copy.