You don't have to self host it if you scroll down there is a list of public instances: https://rss-bridge.github.io/rss-bridge/General/Public_Hosts.html

Reason to self host, some websites don't like rss bridge because it's a kind of adblock from their point of view, and they actively block the ip addresses of these instances. If you selfhost it, you can use these sites, because a single user instance won't generate as much traffic than 1000 users, so they won't notice your instance