There is some valuable information in this book, but it's mixed in with a lot of stuff that seems dubious or wildly speculative, and it's written in a fairly irritating manner. The author's outrageous claims about the many virtues of editors comes across as bizarre and (given that she is an editor herself) narcissistic. The language use and tone also seem very arrogant and condescending, as though she believes that she knows everything and her readers know nothing. And she continually writes "pix" instead of pictures, which I personally find incredibly irritating for some reason.
She also gives the strange impression throughout that she thinks that computers are some kind of passing fad. She seems to assume that an editor's work will mostly be done by hand in hard copy, rather than using a computer, and seems to write off ebooks as being clearly inferior to and less popular than print books. She states, for example, that readers of novels will always prefer print, and doesn't even attempt to justify this belief.
And as with everything in this book, the tone seems to suggest that Mackenzie has a very strong belief in the correctness of her own opinions, like if you were to suggest that she may be wrong about something she would simply dismiss it out of hand. I've never met her, obviously, that's just the (possibly erroneous) impression I get from this book.