Ken Fisher does go way overboard on the marketing. Does that necessarily mean he's a poor investor?
I know his book Super Stocks was one of the first stock market books I read and it made a big impression on me.
These guys independently and consistently rate him as one of the best forecasters they follow:
"He has been clear and consistent with his guidance. His speculations about the magnitude and/or direction of future changes in the overall market are right about 72% of the time, a very good track record."
http://www.cxoadvisory.com/gurus/fisher/default.asp