If you were not helped by the study materials you already bought, then don't buy another study guide.
DAT Destroyer is a study guide. It has practice questions with detailed solutions.
Some people's learning style is to study on their own. If study guides/other materials don't help you, then save your money and don't buy more.
Plenty of people take the DAT after studying on their own or even after not studying much at all. If you're motivated and bright, that may be the route for you. And as a disclaimer, I'm not saying that people who buy study guides are not bright (ie - I bought the DAT Destroyer) Everyone just has to figure out the way they learn best.