Good and all, but as somebody mentioned on the Masto comments this shouldn't be needed, this is taking an open JSON file and turning it into a proprietary Google-only format so that Organic Maps can import it, that feature should be on the app itself already.
Also as you're uploading that data to a random website you're effectively doxxing yourself as your important addresses likely will be there, your home, your workplace, etc.
Edit: Was mistaken and corrected below, the format IS a standard, not proprietary, in addition the author answered in Masto clarifying that all the conversion happens in the browser without uploading anything. That said, i do insist that the app should support uploading in this geojson format, specially since it's what Google Takeout gives you
I understood it was Google-only, great to be mistaken about it. Still, the app should also support that geojson importation format too, there shouldn't be a need for external tools, SPECIALLY since it's what Google Takeout gives you, this very much should be a feature of the app.