Anything that tests your knowledge is good, because it gets you out of your usual study groove. Even if the questions are more difficult, it might still make you consciously aware of areas of study that you need to work on.
For example, the question might be way too in depth for you, but if you can't recall 5 or 6 general items dealing with something in the question, then you probably ought to study that area some more.
Kaplan is the sure thing for the DAT. I still believe you can memorize that book and get scores about 20s in every subject.