I took the practice DAT from the ADA website the night before my real test and scored 4-6 points higher on each section than I did on the real test THE NEXT DAY. I think its probably easier becuase the practice materials have geared themselves towards it and the types of questions are discussed on this website to overkill.
I suggest you just study as much as you can stand, but really understand that probably 75% of the real test was answered from material you'll remember from school (or kaplan)...and maybe the other 25% was the obscure stuff from destroyer or top score practice questions. If you do well in your pre-req's you are fine! If not...study more 🙂