I just got the three books last night and perused through them for about half an hour. Some of the questions overlap from the paper tests the GMAC sells on the mba.com site. In addition, there is also a diagnostic test provided for each section on the beginning of the comprehensive OG book. So it provides you with a specific test for just the SC, CR, DS, PS, and RC sections. Then based on how many you answer correctly per test, it gives you a table to determine whether you did "excellent", "above-average", and so on and so forth.
The explanations to the answer choices seem to be clearer than the 10th edition. There are also "myth busters" in parts of the book to derail any common misperceptions about the GMAT. The one that caught my eye was the fact that the first 10 questions aren't as important as people make it out to be.
Just based on my very little exposure to this book, I feel that the OG 10 and OG 11 and its supplements would probably suffice as sole sources for a good overall GMAT review. Of course keep in mind though that neither of these books really provide you with tactics on how to tackle the test. They just provide you with practice questions and answers. I am using GMAX online and will probably try to use this 11th edition as my primary source for review for my test in October. I've been through the 10th edition already (not a first time test taker).
I'll keep you posted on how I fare.