Just wanted to provide some more info on the background service worker, though if you've pulled the code you've probably already seen the same.
Right now that worker does two things. It redirects to a survey if you uninstall the extension (going away in the next update once it makes it through the webstore review), and it allows detection of the installed extension since its required in Chrome unless you search from the url/navbar.
And just so there's full details on the restriction here too:
We determine if the search is from the url/navbar only through that fromSearchBar query parameter, so either manually entering the url without that query param, following links without that query param, or by setting your default in your settings manually and searching from the url/navbar will all work. It is just that search bar on the page that gets disabled without the extension. There's also no restriction right now on non-Chrome browsers or in a Chrome Incognito Window.
Thanks for digging in, bringing that up for clarification, and for your proposal!