I used both as references, for class and the DAT. I found the first book to be more useful than the second for the DAT, as it was more involved in the foundation. The DAT, at least when I took it, seemed more focused on concepts, and foundational stuff, rather than seeing how many advanced mechanisms/rxns you knew.
I recommend both highly for the class and the DAT. I would not spend too much time working out every problem in the 2nd book for the DAT, just use it for your weak areas. I think anything that is in those books is fair game for the real test. I found them right up there with Chad's Videos and DAT Destroyer as far as helpfulness.