5.56 is not exactly hard to group at PDW distances full auto. But the whole PDW argument goes back and forth all the time.
P90's and 5.7 aside, I'm not sure what real use this pistol fills. I mean it's a neat piece of gun-building, but probably heavy fully loaded, and I'm not sure having 50 rds in a handgun is worth that size, weight, and reload speed penalty.
Neato gadget though.