I just began the eighth and final section of French. AMA.
I figure I’ll complete the course in two or three months. Then I plan to go back and “legendary” everything in Sections 7 and 8, which might take another several months.
Am I “fluent” now? No, but…
Can I function pretty well in French? Yes! I know that I still sound like a young kid when I speak, but I can communicate. I can read novels intended for adults. I read a lot of my news in French media (La Presse, Journal de Montréal, Radio Canada). I listen to Radio Canada and understand most of it. I can watch movies and shows, but French subtitles still help when they get talking too fast and/or colloquially. And I write emails to Québécois colleagues, using a grammar checker. But most of the time my grammar is 95% correct anyhow.
Have I only used Duolingo? No, but it is a regular part of every day and it has been helpful. I also (as per above) use various forms of comprehensible input. I have taken a university course. And I have a weekly session with a tutor. And I’ve traveled to Québec several times for business and pleasure.
Is Duo useful? Yes. And more so if you use the paid version. But the key — Duo or otherwise — is consistent, daily effort. Duo + input + tutoring sessions mean that I’m immersed in French about two or even three hours a day in average.
Where do I see myself in a year or two at this pace? Probably pretty close to what most people would consider fluent. I.e. fully competent and comfortable in a French-only setting.