i actually ended up scoring better on the real thing than topscore&achiever but i think both were pretty good for practice...
i used achiever to jump start my studying cause it'll really let you know which areas you're lacking.. then i used topscore to get some confidence before the test... i spaced them apart and took the 3 topscore tests about 2 weeks before the test.. i think something like 2 weeks before, 8-9 days before, and 3-5 days before..
i felt like some of the DAT questions were somewhat tricky and required you to think like achiever problems... i think topscore qs are more straightforward... to feel relaxed&confident during the test i think you should be able to do the achiever probs pretty well...