I am just about to return to the US after 4 months in Buenos Aires. I lived in Peru for a year and a half leading up to April 2022. I'm probably approaching a B2 level of Spanish right now (based on my experience attaining a B2 and then C1 level of French once upon a time).

Interestingly, when I was starting out, I was in Peru with a Spanish speaking significant other, and using Duolingo as well as taking private lessons. I found as a few others have mentioned that Duolingo actually got in the way. I liked the gamification. It helped me practice, but there were so many exercises for each set of vocabulary. Due to the way their system worked, I had to go through a lot of exercises that weren't useful for me because I had picked up the content with other learning methods. You can test out of things, but if I wasn't ready to test out of the whole block I still had to go through a lot of material that wasn't useful (i.e., even testing out skill by skill, was tedious and time-consuming and counter-productive).

So as discussed in the article and here, Duolingo can't get you even to a low intermediate level, just the basics. And I found that it doesn't pair well with more intensive learning. Maybe other people have had a different experience, but I think it's good for the light hobbyist until they are ready to move on to something more serious, but that's about it.

I also worry that it's promises and gamification trap and frustrate people who could have done more. Maybe it makes up for that by getting a large number of people started who then go on. Maybe.