The idea is cool, but, well:

"No account, no server, 100% private — everything happens in your browser."

Your post makes it sound like you consider this a bad thing?

I don’t see the downside here.

If you don’t believe it, maybe disconnect from network before dropping the file?

Are you implying that the lack of data harvesting is a disadvantage?

It not a disadvantage but a rare trait nowadays.

sound great

well makes sense if JavaScript is run 100% locally.

Browser can be treated as loader of code to be executed only locally with Local only data.

i hate js, but it's doable