@ikt

If your primary concern is that a product is "free", and you don't care about the quality of the product, or about a corpus of valuable knowledge disappearing from the web, or about the exploitation of both volunteers and contract workers in the creation of that product, then yeah, I guess it is "amazing".

The way Duolingo was developed initially, it's like Wikipedia suddenly locking all of its information down, shutting out its editors, and replacing its website with an AI app that you can ask questions of while you get served ads.

You have no way of knowing the accuracy of the answers, you can't edit it, you can't search, you can't look at the sources. You just have to trust it. But hey, it's free. Quit complaining.