No gun will not function reliably with poor mags, an issue with HP magazines. When I was shooting mine in IPSC, I had several mags that had to be scrapped after repeatedly being dropped with rds remaining when mandatory mag changes were required. This forces the top rd to be forced through the mag lips in a way they were not intended. Any one who has ever dropped a mag on a hard surface knows what I'm talking about.
I was gifted with a whack of Inglis HP parts by a retired armourer only to find out that they were useless on my commercial Brownings, except for a die that reformed the mag lips. You put the mag into the die and hit the base with a mallet. It reformed the lips but the 'fix' didn't last long.
The quality of the mags had a great bearing on the trigger pull due to the design function of the mag disconnector. If the mag surface was not slick, it caused friction. The degree of friction varied from mag to mag.
As for Canadian SMG ammo being loaded "hot", that is a myth. When the means of establishing if loads were "Major" or "Minor" was the Jeff Cooper "Power Pendulum" (impact plate), Cdn 9mm ball barely made the cut. Cooper himself chronoed some at his "Gunsite" academy and pronounced it on the "cool'' side.