I adore Duolingo! I even feel as an ambassador because some of my friends also join studying after me.
What I like the most is that Duolingo constantly evolving their mechanics. So you won't be bored.
I'm with Duolingo since 2016, finished Italian course twice! And now I'm also have more that half of a thousand streak.
Duolingo helps me to be multilingual
Decent as a crutch for learning languages, although you should also practice the languages outside of it. It can be unstable at times, although that seems to be improving in recent versions.
My phone's language setting is in English, but I still want to learn English using Duolingo. However, the app doesn't allow me to select English learning options without changing the entire phone's language settings.
Duolingo is the only app that helped me develop a habit of everyday language learning, which is essential if you want to succeed. Love the app for all its educational content and teaching approach.