Re: K4 - yes the 30mm is hard to use. I often go back to the G14 myself, just for the 20mm cannon.
But the K4 is a beast in performance, just ask guys like Agent360 and Scotch. If you never learned to energy fight, the K4 will teach you. Leaving your opponent low, slow, and unable to maneuver while you swoop in for a corner velocity tater shot is the K4's forte...