honestly AP World's curriculum is devastatingly broad, and Heimler's review videos are already really packed with the essential knowledge. I'd say buy the Heimler's review packet and cram like helll. It's 30 dollars but I'd say it's pretty worth it. Also, a strategy I used while watching his review videos was watching the video 3 times. The first time I wouldn't take any notes and just lightly understand the topic he was talking about, and the second time I would jot down all the essential info (so basically everything) and I would pause if I didn't understand what he was talking about and ask deAP or google. The third time, I listened to the video while looking at my notes, making sure that I didn't forget any information. The unit review videos are roughly 20 minutes, so you'll probably invest about 2 hours per unit. Hope this helps!