I'll have to disagree in part. I didn't buy them and I don't think I will. But, I tend to be very selective in the books I actually buy anymore. The county library carries a good selection of major sci-fi and fantasy works, so I can usually get my fix for "free".
Still, I think the books have been a good read so far. I've had some issues with a few things, but still an entertaining story and it makes for a very interesting background to the original Dune books. I think I felt a stronger attachment to the three House books (Atreides, Harkonnen, Corrino) but that was becuase most of the characters were familiar where the Jihad books are essentially all "new" characters.
Of course, I'm hoping all this warm-up work will give the ultimate payoff when these guys write the final book of the Dune series (the sequel to Chapterhouse: Dune that Herbert wasn't able to write before he died).