This is a nicely polished app for helping to learn your hiragana and katakana. Right off the bat, there is a clean (if a bit monotone) interface and a very helpful set of kana cards. The cards themselves are crisp, large, informative, and nice-looking. So why only three stars?
Well, the biggest problem I have with this app are its tests. You can choose a writing test or timed identification test. With the writing "test", you trace the pre-drawn lines in order...and thats it. With the identification test, you select one of four possible syllable choices underneath a given character, with a time limit.
Both of these are fine in their own ways, but there is no way to just kick back and practice your kana casually. What Id like to see are two more modes that each would correspond more to using actual flashcards. To practice writing, give the user a sound and provide a box underneath it in which they can write the character. When theyre done, they can tap a button to fade the flashcard character into the background of the box, possibly in a different color. To practice identification, display a character and provide a keyboard to type the sound into, no time limit. Compare with database to see if correct. Simple, effective, relaxing. Not everyone learns best under the clock.
To conclude, this is a nice, polished, and advanced app. However, dont neglect the simple stuff. Id expect that for being more pricey than most of the other kana apps.