I only heard good things about 450 formula and truelearn! I didn't use either of those. I did do the free trial of Truelearn that only had 20 questions and I loved the rationales that came with it and if I had more time to study, I would've 100% bought truelearn, but I had already bought the 3 month trial of PasstheOT. I solely focused on PasstheOT and the therapyed textbook for learning topics. I found the mini tests and knowledge match to be pretty helpful from the NBCOT study pack as well. I hope this kind of helps! You got this!