From my experience, the first time i took the DATs, all I used was kaplan to study. I personally feel that their grading is quite a bit inflated. Taking their practice exams, my scores were around 19-21 in the sciences. When it came time for the DAT, my scores were quite a bit lower. In that sense, don't fool yourself into thinking that if you're doing well on the kaplan exams, you're good to go
Opposing that viewpoint, the second time I studied for the DAT, I used achiever, topscore, destroyer, crack dat. What I can tell you from using all those sources that pertains to you is that achiever is a lot harder than the actual exam. I remember taking an achiever exam a few weeks prior to my actual DAT and still getting like 15-16s on the sciences. It didn't do a whole lot for my confidence haha. So just remember, not to get discouraged; especially with achiever.
What I did like about kaplan is the huge amount of practice questions that are available to you. If you study them properly (i.e. make sure you understand the wrong answers along with the right answer for each question) you should feel a lot more comfortable going into the exam.
Hope that helps. Good luck