I'm really happy to have found this product. I just started using it to improve my Russian speaking skills. This is so far the only gptchat that supports this language.
I enjoy the interface for its simplicity - no room to get lost. It is missing, however, methodology and gamification to keep you motivated and working towards a goal. But overall, it's helping me pinpoint my mistakes in syntax, vocabulary, and pronunciation.
PS: A native mobile app would also improve the user experience. For example, the voice-to-text functionality is still buggy on mobile.