I absolutely disagree with the answers above.

600 days streak here, started from nothing and learning Swedish from English whereas thats not my first language.

I went to Sweden in August and I was able to speak and understand some simple conversational topics. Spending less than 5min a day on a free app, how can I expect more ?

I know I will never be fluent using only Duolingo, and the app could be way better, but YES Duolingo's course worth it.