Use it for practice on the PAT, honestly if you memorize the whole DAT destroyer you should be fine. Also read the explanations in the back of the destroyer. Simply doing the problems in the destroyer just isn't enough. I am finding more things that I need to work on by reading explanations to give me a thorough understanding of the topics that I may be weak in.
I personally didn't use achiever for sciences. I believe Bootcamp and Qvault are better for that (worked for me). However, I have heard good things about Achiever's PAT, which is known for being really hard so if you can get through that, you shuold be good.