I actually thought the questions in Cliff's AP and Barron's AP were great prep for the test. Some of the questions I had on my actual DAT seemed to be quite similar. I did the questions at the ends of the chapters, but I didn't do the full AP exams at the back.
The Destroyer gets into nitty-gritty details and is more difficult than the real test. Also, in the bio section, it seems like half of the darn questions have "all of the above" as the answer--this is easy to catch on to and gets annoying.