Here's my update:
As I've found in other DDF threads on learning languages, DoC among others, pointed out that Duolingo is good for vocab, but not so great for grammar. I used it for Hebrew for a few weeks consistently on the train, and I agree. It's a fun app, but I don't feel like I can have a conversation any better than I was able to beforehand. I thought this would really help since I already have a background in Hebrew, but it didn't. Add in the fact that the brain can be quite good at figuring out games/puzzles, and I was often able to guess the correct answer even if I didn't know the true definition of a word/sentence, and it was time to stop using the app.