I like that you keep it wholly on-device - that makes me feel more comfortable using it. Is there a way to point it at existing samples of my writing to help train it?

And can it be different per app?

For example, I have a novel. I would never AI write a novel but autocompletion is fairly reasonable. My writing there is notably different to an email. If it was active in Scrivener, I'd want it to be using Scriven writing samples for consistency.