Ask HN: Feedback for quiz-based learning tool

Last year, I got the chance to meet my wife's extended family in Japan. However my Japanese vocabulary was nonexistent. So I built a prototype tool for myself to learn new words. Recently, I decided to try and make the service useful for other people. So over the last week or so I've prepared and launched the prototype at mrflashcard.com. The primary feature is a quiz-based study mode, where the questions get increasingly more difficult. It's running on Google App Engine and costs little per user. My plan is to offer pro subscriptions or to sell companion iOS and Android apps that have offline syncing. If anyone here has a few spare minutes, I'd love to get any feedback from them. After clicking "Create new Deck", there is a button to add some example cards to try out. Thanks for taking a look!