How about the recoil effect. Now The Rockland 22TCM seems to be made with metal and the last tech report I read was that It is loud but the recoil surprisingly less than what one would expect from that kind of a gun. I suppose long barrel vs short in the same caliber also effects recoil. I don't trust poly guns just because plastic has a tendency not to take stress too well with +p ammo.
Weight, barrel length, Velocity all effects recoil.
A heavier firearm well recoil less then a lighter one all else being equal.
A well design poly firearm well go as many rounds if not more as a metal one.
All moving parts are subject to stress the more stress on them the faster they wear out.
Their are plenty of all metal hand guns that are not plus p rated.
Their are poly firearms that are plus p rated.
I trust firearms from the major manufactures.