The existence of a menubar icon as an option implies it’s a service that needs to run all the time. I compare that perception to what uBOL mentions in the App Store description.

> uBOL is entirely declarative, meaning there is no need for a permanent uBOL process for the filtering to occur, and CSS/JS injection-based content filtering is performed reliably by the browser itself rather than by the extension. This means that uBOL itself does not consume CPU memory resources while content blocking is ongoing -- uBOL's service worker process is required _only_ when you interact with the popup panel or the option pages.