This may not be a so called flashcard because it does not use images.
The originality of this flashcard is that you answer with your voice.
The correct answer is not chosen among several candidates but has to be answered by your own voice.
Thats why the posibility of a lucky guess would be low.
Besides, you have to pronounce exactly otherwise you cannot get "correct answer!" I believe that this app is very helpful to memorise both Japanese and English words.