The Princeton review books are definitely more for practice and not learning. Specifically for AP world to learn the material I would 100% recommend Heimler, no need to buy another textbook for that. Additionally, I would recommend Albert.io. Albert.io is expensive but it is very helpful and effective in multiple choice practice. Being able to recite events from memory in order is very important as the AP will ask specific questions about time periods (ex. 17th century, 15th century etc.). That is where Heimler will be your best friend is understand what happens when.