I had picked up a police surplus PC40 in barely used condition a few years back, with ghost ring sights it was good for 2-3 moa at 100 yards, pretty impressive, chunking 180gr .40 rounds out at > .357mag velocities, fast as I could pull the trigger with no noticeable recoil it was very easy to keep on target. Of course being a Ruger it was heavy and built like a tank, well balanced but ultimately the heaviness made me ditch it, well that and getting rid of my .40 handguns (simplified down to 9mm, .357, and .45acp for now). I think these things definitely have a place, if you live in an area where you only have short ranges, or plan to use it for home defense, it's more controllable under rapid fire than a rifle caliber in the same size/weight of gun, and the ammo is generally cheaper and available even during these 'panics' so you can afford to have fun with it.
If it were possible to get, I'd have an mp5 clone SBR in 10mm, hell even in .40 would be pretty good, would never feel undergunned with that inside a house.