Like some others have opined, when a "European-style" magazine release is referenced, I've always assumed that a mag-release catch was located on the heel of the butt. Now that this bit of confusion seems to have been cleared up, I would make the point that a European-style mag-release located on the butt of the pistol does have a couple of potential advantages over the "American-style" mag-release, located behind the trigger.
Firstly, though (everything else being equal in terms of training and use) the thumb-operated, frame-located mag-release is no doubt faster to deploy than the heel-release is and can be accomplished one-handed, I think the butt-located mag-release is less likely to be deployed inadvertently (the catch does not ride against the holster continually and it usually takes more effort [and, yes, for the same reason, slower] to dis-engage).
Secondly, as writer/firearm expert and le officer Massad Ayoob pointed out, in cold weather, when people are more likely to be wearing mittens or gloves or have cold, stiff fingers, "...I found that with heavy snowmobile gloves on, the cruder gross motor movements of pushing back the latch with the free hand thumb and ripping the spent magazine out were actually more easily accomplished than finding the magazine release button with a thumb encased in a heavy glove that blunted the sense of touch and limited the thumb's range of movement. In short, in heavy winter garb, I was able to reload the P-220E (with the butt mag-release) as fast, or very slightly faster, than the P220 American."
Regarding the "paddle-style" mag-release, I've come to really like the one on my HK USP40 pistol. I find it just as easy to dis-engage the mag with the index finger of my shooting hand as it is to use my thumb.
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