The book is described as a case study of Jonathan Barnbrook's Priori typeface. As such, it might be interesting, and may also offer some insights that might be applicable to designing other typefaces, but I suspect it should be considered how to design a -- one, particular -- typeface.

The title is quite deceptive; as John pointed out it is a case study in the design of one typeface. I would add that it is not an especially interesting case study. Unless you adore Barnbrook’s work it is a waste of $15. Do yourself a favor and find a copy of Doyald Young’s Fonts and Logos.