I carried an M9 as a crew chief, now I have an M9 as an MP. They work fine and are plenty accurate, but they are huge. I would gladly give up my M9 in order to carry an M&P9 or G17 or XD9. The 9mm does just fine and is readily available. I would change because any of the other three options I mentioned are sized for normal people. The M9 has a very long reach to the trigger. The M&P9, with it's adjustable backstraps, is able to be tailored to the person. I'm 5'10-5'11 195 lbs, so I'm not a small guy, but the M9 is too big. Any of the polymer pistols would fit a greater number of soldiers, making them more effective with their sidearms.