Hi lark,
I have the book in front of me. I haven't actually read it, but as I look through it, it seems like an interesting thing to have if you like the deck, but not vital to have. It's not written by any of the authors/artists of the deck. It's basically a short introduction (which doesn't say anything about how the deck was created), then a page per card giving a description of various elements on the card and upright and reversed divinatory meanings, and then a section at the end with 12 different spreads. In a nice touch, each spread has a short sample reading with that spread.
There's a page at the end which gives bios of the authors/artists, and I found it interesting that the illustrations for the Minors were taken from the work of Richard Doyle, a famous illustrator who died in 1883.
The book seems nicely written, but again, it doesn't seem like something you really need to have, unless you're absolutely captivated by this deck and must have anything in print that relates to it. I don't think you'll be disappointed if you get it, especially if you work with the deck a lot.
-- Lee