A couple points based on 10 minutes of trying:

1. I selected "advanced level" for my target language. I expected real sentence. Instead I got a lot of "I am American" and "He is tall" type sentences.

2. In some cases when I was asked to select the word to complete the sentence, multiple options could be correct, but only one was recognized as correct by the program. Concretely, the format was "He is ______" and the possible solutions were "that" "Indian" "American" "comes from" and "French". Three of those options are perfectly grammatical, but only "French" was marked correct.

3. No offense, but this all has the hallmarks of AI slop, which I consider to not be an appropriate way to develop language learning tools, especially at an above-beginner level. Each language has different structures and complications and requires attention to different aspects of the language.

4. Above all, this app does not appear to differ from Duolingo in any substantial way, except that it's worse. If you're going to boast that your app is better than Duolingo, you should substantiate that with a concrete argument. Certainly Duolingo is highly flawed, above all in its total absence of formal grammar instruction which is something that even an AI-generated app should be able to do.