Destroyer is a book filled with practice problems. Most people use it as a learning tool by taking advantage of the detailed explanations for each question. However, the questions in Destroyer are of higher difficulty and you should first build a solid foundation of the material before you start Destroyer. Bootcamp (3 month subscription, although i think it can be extended longer) contains instructional videos and resources to learn the materials (they have gen chem and ochem videos and good PAT practice). However, the best part of bootcamp is the full-length practice tests. Bootcamp is very similar to the difficulty of the real exam and you should use bootcamp as mostly a learning tool (there are amazing explanations for each question), although the practice exams are also a good way to see how you are doing in each subject.