There was another one in f-droid (or at least it was named differently at the time) that I had installed and running by curiosity a few years ago. I more or less forgot it until one day while I was driving on the highway and got forcibly directed out because of a blockade set by protesters (nation-wide protests by farmers occurring at that time). Once in the vicinity of said blockade I got notified unequivocally that something weird was happening to the cellular network. I guess law enforcement people were using IMSI catchers to monitor protesters.

Just anecdotal evidence, however, while I almost never got false positive alerts from this app (once at the arrival of an international flight), the one time it triggered a notification, it was in a highly probable situation.

Communication between our devices and these base stations being so opaque (closed-source baseband processors/OS not helping there) and sensible, I'm glad these projects exist and I just installed this one, blaming myself for not doing so earlier.