While on a recent photo shoot for BIF, I needed to research my D800e settings to match the ones the trek leader was recommending based on his Canon bodies. I had David Busch's D800 book with me as well as Thom Hogan's eBook. I quickly gave up on finding the references I needed in David's book, and switched to Thom's eBook. There just are not enough index references in David's book to enable quick searches for things like AF lock on. I was able to do electronic searches of Thom's book and find every reference I needed. If I found a similar reference in David's book, it did not provide more information than Thom's...often less info.
I don't have DD's book, so I can't say how it compares with David's and Thom's.
Thom's info helped our trek leader understand Nikon features better than he had ever understood them before. He may even buy a D800e.