The problem with looking at words is that you are learning language to language translation instead of language to thought. When I think of "pencil", I have a schema of a pencil appear in my mind. When I see enpitsu (well, the hiragana or kanji for it), if I have to think "pencil" to bring up the schema of a pencil that is an extra layer of thought that slows one down. With more abstract concepts there might now be a better solution, though with more abstract concepts you also have greater issues with things not being one to one translations.
>Just use flash cards.
That is effectively what the apps are mimicking and what I am using. What I'm bringing up in a desired feature I haven't found (granted, I've only checked out a dozen or so apps which is worlds apart from serious market research). As for why I use an app over flash cards? Phone is more convenient and always on me. Also, other than a stack of the most common kanji, flash cards don't really scale in a portable format.
But I probably should buy a deck including kanji for at home usage.