The older digital copies are essentially the same content, but the published version is cleaner, much better written and organized, has additional info, and also is a hell of a lot easier to read. Its also been edited better and has an index. Personally, for 27 bucks at amazon.com I'd say its a worthwhile purchase if you like what you see. Although you can read the first 100 pages of the final published version online--I'd start with that rather than the older version if I were you, at least for the first chapters.