I was taking a Japanese course couple of years ago. The course was difficult and if you did not pass mid-term and end-of-term exams you had to repeat the term which costed a lot of money. Fearing that I could fail I decided to invest in Anki. Needless to say it was the best spent $25 ever.

$25 is surely expensive for a simple app, especially if you are a student without a steady income. But if anyone wonders whether Anki is worth this much money - try thinking of the potential benefits.