What makes Duolingo unique for learning?

Hello! I'm a foreign language teacher who often uses Duolingo as a tool to assess my students' language proficiency. What do you think is their unique approach to teaching? Do language lessons in a playful way make the learning process fun and interesting, and do students enjoy it? Given your experience, do you consider Duolingo to be a reliable resource for both language teachers and students, despite occasional disruptions to their assignments? When you contacted them, did they quickly correct errors, ensuring a smooth experience for you?

I'm sure there are many other platforms for learning English now. I've never learned on Duolingo.