While I not shot a PC version of the M&P 22, I do own the MagPul version in FDE and unless you shoot competion, I don't think the PC is worth the extra bucks.
As mentioned, there is some 'flex' because of the polymer construction and most any gain in accuracy with the barrel is lost.
These are not supposed to be target grade .22s, but are fun to shoot and a training tool for a center fire AR. Mine is certainly accurate enough, with good ammo, for my purpose. I also have acRuger 10/22 that is pretty accurate, I'm not a good enough shot to to see much difference.