If you're rebuilding the engine, wiring, wheels, frame, fork, on a K0-K6 and want to learn a lot of arcane CB750 lore the book is invaluable. Lots of color photos, great tuning tips, and simple upgrades you can make.
Coverage of the F-series, particularly the 77-78 is scant however.
It won't help a lot if you're trying to restore a bike to "factory correctness", it doesn't really cover the subtle cosmetic changes over the model years but it goes into great detail about differences in the engines, wiring, etc.
More the working "guts" of the bike. (The important parts!)
Books like this cost more because of the level of detail, research, print quality, and low print run.