Actually I use this app along with the Zen Brush app to practice the digital calligraphy. Hard to find nice, sophisticated ink brush style calligraphy these days.

50音 is good. However, the app needs to add a layer of mixing-up. I prefer to mix the word order as to retrieve better. It is better for my brain to learn by joining the meaning and connection, rather than just to study one single letter at a time. I like to mix and learn connections of words. The method sticks better. Making more mistakes will enhance my brain while searching for answers. I hope the developer can let us mix of cards of our choice (or preset mix) .... all words, sentences, all Katakana, and all hiragana. In real life, Japan billboards and signs are mixed with all forms. Japan is the only place on earth like that. It is like living inside the pinball machine, the pop art signages are everywhere. Our visual and mental perception have to be prepared for that. Confusion is a good things, it is the only way to narrow down my mistakes made. Going thru this strange process of clarification and regrouping will help the Japanese words to stick better and prompt faster.

This is by far the best app for hiragana / katakana studying I've seen yet!

The most sensible way to learn Japanese.