Not sure who I bought the book from, but it arrived easily enough. The book's very good, but the author obviously tried at a slower rate than me. By the end of the walk I was dead on my feet (which were already dead).
I did the GR20 in May, lots of snow but had whole days to ourselves, would recommend that. Even in May the heat was occasionally too much.
When there's no snow it's true that you don't need the proper maps (which I carried), but should you wish to improvise, or just better understand the route ahead, get the IGN 25000.