For me this is great for practice (I tried Russian). However the big missing piece for all these language learning apps is the lack of support for spotting and correcting errors in your pronunciation - as long as you say the word more or less right, the transcription gives you a pass.
I am very excited for the whole STT/TTS to go away and for us to have models that really "hear" exactly what you said.
Sometimes this is about accent but a lot of the time, the AI won't spot areas where you e.g. fudge a case ending or the stress on a word. Yes, you can get some of that pronunciation right by the AI repeating back with the correct stress or clear case, but you never really get the confidence that you would get from an actual human.
Another product suggestion - turn off transcription (at least for the tutor side of the conversation; I'd suggest both). Personally I find it distracting at best for languages I already speak well and a crutch for those I don't.
Finally, I find it really very hard to enjoy having a random conversation that's not very directed ("What interests you most about artificial intelligence?"). I'd suggest that there are ways of making it more goal focused without being explicitly gamified - maybe something like, here's a position and you have to persuade me (AI debate club!), or something that brings out an actual opinion or relates to a concrete experience ("what's your main goal in your job this year").
Overall though this is the first product I've seen in this space that I might actually use, so well done.