I used the Private Study Buddy for my Private written, got a 95.
My new friends who are all in instrument phase used Sheppard Air for their tests. Don’t expect to learn everything perfectly for the test. You’ll learn via the ground school videos and during flight. The point of Sheppard Air is to get your written out of the way, so you don’t have to think about it while studying for your flying, and eventually for your checkride.
The thing with Sheppard Air is I was sitting there for hours just reading questions and answers I felt like a zombie. They basically have you read an entire section with the question and just the answer then you go back and read the question with all the answers and I guess for most people that works but for myself i was falling asleep on my iPad so i couldn’t really focus.
Based on chatting with the other guys, they only did maybe 2-3 hours a day, and not necessarily all at once. Especially now, since you haven’t started the program yet, take time to pace yourself.