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On the Glocks, the slide release is VERY hard to operate if an empty magazine is still in place, as the follower and spring are putting upward pressure on the release from the inside. Once the empty mag is removed, most Glock slides release fairly easily. If you want a larger and easier-to-use release lever, one is available from the factory for about $15 (same unit that comes stock on the G34/G35, if you want to see what it looks like).
The Glock is not fully cocked until the trigger is pulled almost to the release (firing) point, so no decocker is needed.
Ambi mag releases are over-rated, in my opinion; using the trigger finger is just as fast, and possibly more sure, when a person is talking about weak-hand manipulation. Most lefty shooters learn very well how to get along with right-handed controls; I know this too well, as I've been beat by many southpaws using righty guns in shooting competitions.
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)