I have a Shield .40 that I carry and it has a thumb safety. I think it does not matter if you have one or not as long as you train properly with/without it. I have trained to take it out of the holster and the distance between pulling out of the holster and focusing on the target, I switch the safety off. I think it's there for psychological reasons that the gun will not go off if the trigger is pulled accidentally while retrieving the gun from the holster or while in the holster.... but once again, that's a training issue.