I must say that I never found a "clever" autocomplete that really suited me, I just ended up using a rather dumb "hippie-expand" in Emacs that basically tries to complete the word under the cursor using anything it finds in the current file or, failing that, any other open file. It's very dumb but it works regardless of language (including completing plain text in emails for instance) and it's predictable.
I'm pretty interested in your project, the way it seems to be able to learn from the way you type matches my workflow better than the usual "clever" auto-expander. I also have no issues paying for good tools (and $29 is really negligible as far as I'm concerned when it's for productivity tools, my keyboard alone costs an order of magnitude more).
However, and I know I'm probably in the minority here, I won't even consider using your program if I can't get the source. I'm not even asking for a FLOSS license or anything, even if it just came with a tarball that I can't redistribute I would consider it. But as it stands I would be completely relying on you maintaining the code and porting it to whatever platform I may want to use later. As it stands for instance it seems that you don't provide binaries for the BSDs: https://github.com/zxqfl/tabnine-vim/tree/master/binaries/0.... . I'm sure I could get it to work with Linux binary compatibily on FreeBSD but why even bother? What if Apple releases an ARM-based desktop a few years from now and you've stopped maintaining your project? Then I have to replace it with something else if I have to code on a Mac. The price is a non-issue but having to work around the closed source nature of the software is not something I want to bother with.
Again, I know that I'm probably in the minority and that many people on HN have no issues using mostly closed source development stacks but I genuinely wonder if you'd have much to lose if you kept the same business model but provided the source. I mean, if people want to pirate your program I'm sure they'll find a way even if it's just the binary, so I doubt you gain much from that. Then the risk is people stealing your code but is there really that much secret sauce in an autocomplete program? If people really care won't they just reverse-engineer it anyway? Aren't they even more likely to try and reverse-engineer it if it's the only way to get an open source version that they control?
Maybe I'm overthinking this.
Anyway, I hope I don't appear too negative, that's just my opinion. I'm happy to see people working on improving our code editing experience in any way or form, sometimes it feels like we're still in the stone age with our dumb ASCII files and relatively primitive tooling.