They a very predictable once you've learn to shoot with them at 400-800 range (800 only for buffs), and a buckshot of 4*20mm mfg151 and 2*13mm really make an impression on the intended target.
I never flew with external fuel tank in arenas, even after drop, you carry the mount which is heavy.
The A5 should only be flown with 2*mg151 and the 2*20mm FF, and ontop of that 2 bb guns, each type of guns have different trajectories. More agile because of less weight without the 20mm FF and its ammo.