I think the OP meant any "unofficial guide", not necessarily the book titled "The Unofficial Guide"?
I like The Unofficial Guide book, but they are large and not that portable to carry around with you. The main advantage of this particular book is that they have scientifically determined the exact order to see the rides so as to minimize waiting in lines, and that's valuable if you are going at a crowded time. They provide multiple "touring plans" for each park. That's really the focus of that book, IMO.