The DESTROYER will definitely give you the upperhand on the sciences. However, Achiever I hear is great too. I'm taking my test in about 3 weeks, and I plan on getting Achiever later on in the game to get some more practice in. It's just $50 more....I mean I spent $1000+ for Kaplan...I can spend another 50 bucks for chances for a better score.
As far as the DESTROYER goes, I would highly recommend it. I was definitely skeptical at first since it's not some big company like topscore or kaplan, but I would say that makes it even more awesome because the DESTROYER is for the DAT and only the DAT! As for topscore and kaplan, I'm sure they're using the same stuff for MCAT, PCAT, OAT, etc. And Dr. Romano and Nancy are there for you every step of the way. I've got 3 weeks to go, and my plan is to review the kaplan book, do topscore and achiever, and every moment before, in between, and after, do DESTROYER problems left and right over and over. DESTROYER doesn't give you the timed practice tests like the other programs, but I guarantee you the material will be more useful! I was always suspicious, just like how a lot of people are, of how people would come on here and advertise the DESTROYER, but now i know it's just regular students like you and me that used it and is now just helping spread the word about a great product!
GL studying!