Within 4 weeks of class I'd stopped using Duolingo, but I'm still studying and continuing with classes (lessons with a native speaker). I felt that in many places it was inaccurate, prepared me poorly for written conversations with Danes (and don't even get me started on speaking/proununciation), and didn't provide any of the cultural nuance really needed to understand the language and how Danish people construct their sentences.
I guess it's good for vocabulary, but not as good as simple flash cards.
I believe the idea of Duolingo is to "bootstrap" yourself enough into the language that you can read more material about it, and then start speaking with other people to improve yourself with real conversation in real situation. The teacher may be a good addition, but also costs more and may be confusing.
I get that Duolingo is "basics", but it captures a lot of your time that are better spent learning with other means. Off of this, the company has a $1B valuation. They don't charge for their service and it's not really worth paying a lot for. The users who use it the most probably won't pay.
I don't know how they're ever going to justify that valuation.
Online realtime, or face-to-face course in your town with a selection of human teachers. A Platform to match teachers and students.
The platform could simply list professionals (with a fee), or take a fee per minute of course video, or a fee per booking, etc
The actual lesson content is basic, and you'll want to supplement it with broader learning materials and reading in the target language as soon as you're remotely able, but as a jump start from "never spoken a word of this language" to "able to recognize basic grammar patterns, and get the general gist of what I'm reading" it accomplishes this goal quite well, and for very low effort on the part of the user. I can finish my Duolingo rounds in about 15 minutes every day; the hardest part is just remembering to do it. There's something to be said for what they've achieved there.