The Vickers S gun is just a prewar 2-pdr surveyed for an aerial mount, it's rebuilt for the role but basically right off British Cruiser tank. It's a lot more like a battlefield improvisation than a purpose built aero gun. Same deal with the Tetsefly's 57mm, which is right off a British MBT, it's the 6-pdr gun with most of the barrel chopped off.
I'd go with the a purpose designed aero gun from the ground up if I could. Less likely to have unforseen complications in service. What's the ammo on S-guns, 12-rd externally loaded clips? You don't want to be much further away than about 10km from the airfield to the battlefront.