More bugs than should be possible. The developers have completely abandoned trying to fix this app. Any time they break another critical feature, and make the app more unusable then ever before, the devs just pretend that it's a feature. You'll find many of the tests impossible to complete, because your correct answers will be marked wrong, and people in the comments will be complaining that it's been marked and reported as incorrect for 5+ years and it still isn't fixed.