CEFR or not CERF, Duolingo is clearly designed to be addictive but not effective, because if it were effective people would stop using it. Duolingo's goals are

CEFR or not CERF, Duolingo is clearly designed to be addictive but not effective, because if it were effective people would stop using it. Duolingo's goals are not the same as mine, and the best thing it does by far is to pretend (and make me believe) that I am learning a language.