[jcul]

Yes! Language transfer is amazing imo. I found it here on hacker news and it's probably the most effective tool I have found for learning languages.

For Spanish, over the years, I have taken formal immersive classes, finished the Duolingo tree and the reverse tree, spent time in Spanish speaking countries etc. My level of Spanish was good but clunky and I made a lot of mistakes. After finishing about half of the course, I found I was making far fewer mistakes.

I love the etymology background he gives, I love linguistics so it keeps me interested, maybe not for everyone.

I completed the Paul noble learn Italian course, so that I could compare to language transfer. In my opinion language transfer was much better, I found Paul noble's a bit slow and less engaging, for me personally.

[gramie]

I used it for Spanish too, and it really gave me confidence. I went through the course once and was able to travel through rural Panama for two weeks. I plan to redo the entire course (total about 15 hours) soon, to freshen things up after five years.

I think it needs to be supported with other techniques (speaking to natives, watching Spanish TV or movies, etc.), but for taking in and understanding the language it can't be beat.