I tried Duolingo for Spanish twice. First time I didn't do much with it, second time I stayed almost for a year but I started feeling like it didn't provide what I needed. You repeat same stuff over and over in a very simplified manner before you get to more complicated lessons and you don't have an option to train vocabulary with it, at least not in free version, not sure about the paid one. I felt like I didn't progress with it fast enough and choosing obvious answers again and again got boring, ineffective and bothersome after a few months. I need to write full sentences to learn, not just form sentences from words they give me or fill just one word into a sentence.
The one thing I really liked before they changed the app were stories with longer dialogues. They helped me remember stuff better through a particular situation that was in a story.