I own it. I was one of the backers for the kickstarter campaign to get it translated along with other books (their most recent campaign has an FF8 book in it too).
A few grammatical errors aside (translation is difficult), it's a fantastic read. A really good in depth look at not only the development of FF7 and the rest of the compilation, but also a comprehensive look at the timeline for the world and story, which left even myself, someone who has played FF7 so much that I feel comfortable saying there's nothing in the game I dont at least have a partial understanding of, learning a few more things about the lore. For example, the reason why you find the Peacekeeper weapon in an attic in Kalm is because that was originally Vincent's hometown before shit got bad for him.
A lot of what it states in the book is well sourced, either from interviews with the staff or from the game(s) themselves. It is written in a way that you can tell is from a fan's perspective but isnt afraid to call out the failures of the compilation. The criticisms are fair and well thought out, as is the praise thrown at the series.