Since this is a demo instance, feeds might get cleaned from time to time, depending on how heavy the usage gets. There's an automatic cleaning if the feed does not get fetched in X hours, currently ~6 days.
I don't have experience hosting something on Heroku/Koyeb, but it can be hosted on anything with support for Node.js. I prefer to host it in containers (docker/podman), so a minimal debian vps with 1gig of ram is plenty.