Mastery app is the way to go in my opinion. I took boards in the beginning of July and passed. I spent, 2 weeks studying (typical at my school) with roughly 12 hours a day studying Every third day I did no studying to keep from getting too stressed while cramming. So that averages out to about 8 hours a day for 2 weeks. I watched YouTube videos for the dental anatomy section and learned everything else on the exam through practice questions and looking at my sketchy microbio notes for that respective section. I was getting about 58-61% of the answers correct for most of the subjects my first time around on the mastery app. I then went over 2 released exams and 1 test from Crack the Nbde. I didn't time myself, as I answered questions and checked those answers right away. I didn't like Crack the nbde because the questions were too in depth. I think mastery app was most representative of the exam. Right before my exam, I went back over mastery app questions I marked as Don't Know, which definitely helped.
I thought I failed the exam during and after it, but I've heard the same thing from others, so make sure to keep your cool during the exam and pace yourself.