Well...
...I fired a couple of mags through an MK9 on my last range trip. I had one double feed, but in all fairness the owner expressed surprise and stated that was a first with that gun. I've had a fair amount of range time with K9's, K40's, and MK40's and they've all been reliable, with uniformly sweet trigger pulls. Their only downside to me is their capacity disadvantage when compared to the relatively chunkier mini-Glocks and their amazingly bricklike weight for their size.