Duolingo "teaches" alternate tenses weirdly and IMO too late. But it does well for memorizing words, and it has people speaking with actual Spanish accents and forces you to understand them. So it's particularly helpful for me.
This is why I much prefer Fluent Forever. They play clips of words or phrases that sound similar to non-native speakers but are easily differentiated by native speakers. If you do it enough (and have immediate feedback about whether you heard it correctly) you can eventually learn to hear the distinction. For me it was be the difference between being able to read/write in another language and being able to listen and converse in it.
Some examples that I can remember:
Dutch- broek (pants) vs. boek (book)
French- bague (ring) vs. bogue (bug)
I think people should understand that it’s a supplement, and not a solution when you’re on the plane to that country already
Train line names for example, and all the dozens of english words written in Katakana. You also can't learn from exposure if you can't read the alphabet so I missed out on that too.