I have both authors' D700 books and of two I found Thom's to be the most satisfying for me. There is a lot of additional detail which you can either take or leave as you wish. At the end of each discussion he concludes with a recommendation which I find very helpful. Darrel's book is very good too though and seems to be more concise ( though I'm not sure if this is true when comparing print to PDF versions) I'm not a geek by any means but I found Thom's to be very readable and clear.
Re the iPad v book thing. I prefer a Kindle to read. I have both and find the weight of the iPad, it's glossy screen, and comparatively poor battery life ( compared to the Kindle ) make it less satisfactory for me. I know the iPad screen allows illustrations and other images to stand out much better but the above limitations along with the worry of damaging an expensive product mean it is not something I'd take out in the wild; on the beach for example.