I have been using this app for years now. It got me through college and flight school. It is an absolutely essential part of my studying routine, however, it has a tendency to crash fairly often. I suspect that it has something to do with the large amount of flashcards that I have and/or the number of facets with images. I have amended my workflow to only include only 3 facets at most and tend to leave out images. Without the crashes, Id give it five stars. Mentalcase would also benefit if they took some cues from their competitor Brainscape, primarily in the area of simple UI, post studying reports, and "professionally-made" flashcards sets. Overall, I still highly recommend this app and it is one of the main reasons that I buy Apple products.
UPDATE: Im docking a star simply because they do not allow for split-screen usage on the iPad Pro. My workflow dictates that I have iBooks or a pdf viewer on one side and a flash card app on the other. For now I am using Brainscape, however, it has its own set of problems.