The add-on does what is expected (adds the URL to the title bar and nothing more).

Unlike other add-ons (Add URL to Window Title, KeePass Helper, etc.), this one works nice with e10s, i.e. it doesn't cause Firefox to drop back to single process mode. Also FF57+ compatible is nice for being future-proof.

Source in the XPI doesn't have any tracking or anything malicious, I checked it (you can do it yourself, it's pretty short).

It needs some better marketing/positioning since it was pretty hard to find on AMO (but also maybe because it has few users).