My 0.02 worth...

Glocks are great but carrying (legally concealed or openly)
any loaded firearm with the trigger exposed is only asking for a negligent discharge (ND) with potentially devastating results.

I've CCW'd Glocks for 10+ years and still have ALL my body parts due in part to a quality holster which does not leave the trigger exposed.

Outside of competition, you won't find a holster maker worth their salt who design/produce/sell holsters (leather, kydex, whatever) that leave the trigger/trigger guard exposed (SA western rigs being the exception). There is also a lack of retention, also potentially dangerous.