I'm not a Glocker or own any Gaston Glock models at this time but if you want to learn more about custom Glock features & the merits/-s see:
www.glockworx.com www.glockstore.com www.customizeyourglock.com www.glockbooks.com www.boatmanbooks.com
The late Robert Boatman wrote at length about custom Glock features & add-ons saying in the end, it's better to keep it factory stock;
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As noted the Comolonoli(check spelling) safety is the most common.
I'd be fine with the Glock "safe-action" design. I used to adocate the NY-1 Glock trigger(as noted by gun writer/tactics trainer Massad Ayoob) but IMO, the Glock's safe engineering & robust design can be used factory stock.
CF