This is a reference type book which I suspect will mainly be of interest to those planning to ride all or part of the route. In that regard this is a second edition, and it has been meticulously written. I am riding the section from Calgary to Denver so read it for that reason. It is actually only one of two books written as a guide to the route, and the other is pretty old these days. Some great stories and useful information also on the website, www.crazyguyonabike.com which hosts thousands of riders' blogs, including my own.
If this incredible biking route interests you further, then don't miss the film 'Ride The Divide'.
This book is intended as a supplement to the Adventure Cycling maps, though it does have maps in it, which are adequate for planning. A major difference is the day-by-day itinerary, which includes a detailed description of the route each day. Although the "Flathead alternate" in Canada has now become standard and is described in this book (without any special label), apparently the Adventure Cycling guided tours still go the "main route" which isn't described in this book.
I got this book for a planned tour from Banff to somewhere in Montana summer 2019. I only read to the end of day 21 because I will not be going south of Butte this summer.