Not worth it
In study mode, the questions should constantly revolve. Not show the same questions in the same order every time.
In test mode after clicking "grade" and then trying to select a question answered wrong, it takes you to whatever question you were last on. Not the question you clicked on.
All in all this is not a very professional app and the price is way too high for something this inadequate.
Haxors about
2017 FAA Test Prep - Fundamentals of Instructing, v1.85