That Anaconda had a 5 second volley, then ran off. The viper NPC had a few shots in. Not exactly PvP, holding them off..
There are other videos from that guy, not all facing cowardly combat loggers. Not all successful either, mind, but do illustrate that the ship is at very least not a sitting duck compared to the other cargo ships. The SLF does come in handy for distraction tactics against unprepared opponents. That Anaconda only let off a short volley because it went to dispatch the fighter first and that gave na'qan the time he needed to batter it with missiles. Considering the price difference between the 2 ships I think it was a pretty decent demonstration of the Keelback's intended purpose. That said, the build he used probably didn't have cargo racks in it so I don't know how effective of a cargo ship it'd be, lol.