Interesting note about the Serpa retention holsters. My current holster is good old plain leather. However, I'm looking for retention holsters for both my G19 and a full size 1911. At least for the G19 I think I'll favor the ones with the thumb release vs the ones with the button/tab by the trigger guard...
No matter how mindful I can be - I do not trust myself without an external safety. I can manipulate the safety on my Ruger 1911 using only the braille method. It is second nature. Only thing that provides me assurance when a round is chambered and the hammer is up.
I carry GLOCK 9mm +1 all the time IWB. I use a holster with a single large clip. If I am going someplace where I may have to remove it, like trying on clothes or doctor visit, I clear the chamber before going inside and, if necessary, remove the entire holster with gun in it. I do have a locking holster but only use it for hiking and dry fire practice drawing from it before going out.