This looks really cool! I think the UX around selecting a subpart of the text and asking it to rewrite that is very promising (also for stuff like code editing; it'd be awesome to have this built-in to your IDE, not sure if VS Code already has it).

My only worry with this is that I'm not sure what the long-term edge will be. This whole product looks a bit like just a feature that will soon be added to MS Office Word. I'd love to hear more from the authors about how they plan to differentiate themselves here.