[dgimla20]

The process of making decks and the SRS features Anki provides are some of the most effective ways to learn language (particularly vocab) behind learning (grammar) from books and language exchange with a teacher/native speaker.

Duolingo is incredibly limited. If you are serious about learning a language, you should look elsewhere. Duolingo is only a good investment of money if you want to pay for a video game with minute levels of learning in the background. It's sort of like playing Sid Meirs Civilization to learn history.