I have the extended mag release on my G22, and it does not release the mag unless I want it to. I carry it in a kydex IWB rig, and two different Galco leather pancake rigs. Not one time has it dumped the mag on me.
I though the first kydex holster I had might though so I took a little heat to it and made a small dimple relief channel for it, took 20 seconds tops and it is impossible for it to depress the release without crushing the holster. With my current holster I don't think it is necessary. Kydex doesn't need much heat and it is pliable, it will hold the shape you put it in when cool. It is also easy enough to relieve one layer of the leather on the leather holsters too, I have done that for a standard mag release on a Para P14 several times.
Some of us need the extended release to operate it without shifting the firing grip. If we can use it without causing a problem somewhere else there is no harm in having it.
Just remember reliablility above all else is what you are looking for. Keep it simple, but make sure it works for YOU. Put on a good set of steel night sights, an extended mag release, a traction aid on the grip and call it DONE, that makes the perfect Glock for me.