My German was probably pretty bad for a long time. It took a decade+ to get any kind of accent and comfort with the language (especially since I wasn't living there for most of that time). But I was up and running with the language, having conversations, reading the news, listening to podcasts, etc even if I wasn't "perfect." That, to my thinking, is at the core of what I need a language learning app to do - get me to the point where I'm making progress with it and forming my own thoughts and statements, don't hold me back because I mispronounced an accent or missed the gender on a word, etc.
My own experience with Duolingo is that it is ok as a way to memorize some grammar, but the lack of context is a problem. Random sentences just designed to mix in vocabulary don't seem to be as useful as contextualized learning, IE: at the train station, at the bank, etc.