Why should I, as the user, spend time and create cards on a piece of non-free software which I have no control over? What if you stop the service? I tried it for a few minutes, but couldn't find a "export" feature apart from the "email us to get your cards as csv" part. An "export cards and progress" feature would be nice.

I tried adding a few cards, which seems to work fine even in the worst case scenario. It seems to work even in other languages? I haven't tested it enough to comment on how well it does though, but my guess would be as well as GPT does in the said language. This has the potential to be a huge time saver. If it could handle something like a few pages of notes and divide it up, I can see it being the new standard of SRS for many people.

As I said, I can't see myself using any non-free software for something as critical as learning.

It's a good piece, and excellent as far as it goes. You should investigate hypnosis. E.g. you can just remember things, w/o spaced repetition or anything, just transfer a piece of knowledge directly to long-term memory immediately. The tricky part is second-order effects. Once you move naturally-autonomic subsystems into voluntary control you now have responsibility for them. The result is a kind of change-of-being learning as contrasted with accumulation-of-facts learning.