I don't quite agree on sling shotting. You can easily ride the slide (even for a fraction of a second) which can slow down the slide as it is going home. If your recoil spring is weak or if your pistol is dirty (fell into sand and grit and you just picked it up to use it or it has been fired w/o cleaning), this can be trouble. You could add a sharp "tap" after dropping the slide. It's also less consistent.
Using a slide release, you can consistently release the slide and let it go home from its own weight and spring power. That extra distance you can compress the spring when sling shotting can be nullified by accidentally slowing down the slide.
As for the extended mag catch, I can see how it can accidentally be pressed in a carry holster. I probably wouldn't use one for a carry pistol (same as the extended slide release) because if you have to reload your carry pistol, then you're in trouble anyhow.
For a zombie/SHTF pistol where frequent reloads are required due to the number of hostile targets, the stock mag catch is almost impossible to use unless you have uber long thumbs or have a slippery enough grip to smartly swivel the pistol to use the short catch. the extended slide release can come in handy.
my grip on my G17 does not come close to accidentally touching the mag catch or the extended slide release (not even close). YMMV though.
I have rifles for SHTF/zombie scenarios with lots of mags and ammo, but why restrict your Glock to last-resort/personal defense duty? With the way I have mine set up, you could use it as a short range offensive weapon