I found the Q & A books invaluable. The questions and explanations explain what is required far better than the course notes (excellant as OATs are) did and improved my understanding of the subject. I can credit getting above 90% to Keith's books.
I would like to say that I think alot of preparation has gone into producing the documentation and I would feel uneasy about selling my books at a reduced price therefore a lack of royalties to KW. But that is a very individual opinion of mine an I do not expect many to share it. If you do not have any problem with this issue, then buy the books. You will not regret it.
I have just checked my copies of 1000 Q & As. It appears that who ever is selling the copies is breaking the copyright unless permission from the author has been received. Just a thought.