Not that i dont want the tse tse but i dont think it will see that much use, the gun is pretty much only efficient against guns and light GV:s like m3:s and the 4x20 mm of the mk VI is almost as efficient against those targets.
The Mollins will be yhe most powerful flying cannon we will have, by some margin. The B25 75mm gun fire HE rounds and it is much slower. The Mollins was a succesaful field gun in N Africa before it was adapted for naval use and installed on the Mossie. Indeed as tanks got heavier it was no longer considered effective against tanks front armor, but it was still plenty effective from the sides and top.
The 57mm 6 pound AP Mollins shell is a proper anti tank weapon. Dont be fooled by its caliber vs. tank guns, this is somewhat compensated by a high muzzle velocity. It also fires about 1 round per second which allows you multiple shots per attack run.
With the range it will have you can do some serious damage to ships and base structures before you enter auto-acks range. It is not hard to imagine what this gun can do to a bomber from outside of the defending 0.5s range, or from any range

Finally, this thing is installed on a mossie. This means good performance for the platform, much better than 410 and definitely better than B25. It also looks better than any other plane. With the extra weight, it is like our FB.VI with two 500 lbs bombs in the bay. I sometimes dogfight the VI with the bombs still inside, and it pulls 3000+ fpm in a climb.
OK, it is not a Yak3 or spit16, but not a hangar queen either.