The book is titled "Z80 programming for logic design" but would be more accurately titled if the "Z80" were omitted.
Nowhere in this book does it specifically mention the Z80, why you might choose it opposed to other microprocessors, or the specific features of the Z80 being used. In fact, I would hazard the guess that the book is substantially equivalent to the 8080 version of this book.
It is interesting insofar as it talks about bitwise logic and masking, but it really doesn't stand apart as an "essential read" as the other Osborne books do.
My take on it? A big yawn. This could have been thoroughly discussed in a third of the pages.