ive noticed that ppl who had amazing teachers (and they know and understand mostly everything due to an awesome class experience) for their prereqs (and assuming they didnt half-@ss the class), in general they dont need destroyer and all that other jazz and kaplan works for them. they just go through kaplan books and work out few probs and maybe buy few practice tests and bam, they r done and they usually do pretty well too!
however, if your like me and some of ur profs were not awesome like the way chad is, u will be deficient in some areas so u will need a difficult resource like destroyer and etc to help you to think like the way DAT wants you to.
i will tell u this. Chad is the man! I have to retake ochem 1 cuz I didnt do well the first time and I have made an A on both tests so far! In the high range, 97 and above mind you. This is coming from a kid who has never seen A's in ochem ever (I have a track record of pathetic grades in ochem so I cant tell u how aweosme it feels to get A )! And I havent had to practice significant probs and its to the point I can recognize mistakes on my profs test and even that of my TA's in the review sessions (I was even getting bored in the review sessions cuz ppl asked questions too obvious to me hah!) And its Chads vids that have helped me to get to this stage. Now, even destroyer and orgo odyssey are getting easier and its helping me cuz its all about applying what Chad taught me. And no, he didnt pay me to say that, but I wanted to give the man some credit for my A's haha!
moral of story, if you have an excellent GPA and feel u pretty much know the stuff (like really really know it) from your classes (albeit will need to review) then dont need to invest in expensive resources.otherwise, read breakdowns and invest away! ur score is important, do what u gotta do to make it as high as possible. ultimately you know ur strengths and weakenss so buy resources according to what u dont feel comfortable with.