throwaway41968

That's the approach I've had recently. Duolingo into Clozemaster, with generous helpings of Memrise on the side. Too bad Clozemaster is awfully limited in its free version.

I think Duolingo is fine if you're looking to learn a language that's really close to yours. I know French, took up Spanish and within a month of practice I could cobble simple sentences in a casual conversation or text my Spanish-speaking friends. The approach where you just "figure out" from trial and error works well when your source and target languages kind of work the same way so you can just feel your way through it. On the other hand, I suspect that if I wanted to learn, say, Russian or MSA, I would probably be better off with actual formal courses.

I have only given Rosetta Stone and Pimsleur a cursory attempt but they seem awfully slow and expensive for what they do. Duolingo, for all its flaws, is free and fun.

As for your "purely from marketing" comment - Duolingo solely relied on word of mouth for all of its early phase, apart from a single TEDtalk. It's true it may not be as good as many alternatives, but as far as the free and fun factor goes - it is simply unmatched.