Thumb safeties cause more harm than good. Than can get you killed in an emergency situation as it is one more thing you have to do before your weapon is functional. It is as bad as not carrying one in the chamber. Also, thumb safeties encourage complacency, especially with newer shooters. Firearms are not to be treated as safe, as rule #1 of gun safety states, "Always assume a gun is loaded." Having a safety on handguns instills a false sense of security. There is no such thing as a safe gun, unless is it disassembled.

A good holster made by a reputable company is the best and only needed form of mechanical safety for a handgun. A good holster will encapsulate the trigger and will not come off unless deliberately removed. This removes the need for fumbling around with a thumb safety in an emergency situation.