http://en.wikipedia.org/wiki/Jeff_Cooper" onclick="window.open(this.href);return false;Condition Four: Chamber empty, no magazine, hammer down.
Condition Three: Chamber empty, full magazine in place, hammer down.
Condition Two: A round chambered, full magazine in place, hammer down.
Condition One: A round chambered, full magazine in place, hammer cocked, safety on.
Condition Zero: A round chambered, full magazine in place, hammer cocked, safety off.
In order to have maximum effectiveness as a safety/protection device you must carry one in the chamber.
In order for me to feel safe, I want a thumb safety. So, I only carry guns with thumb safetys. (I carry a Taurus 24/7 Pro .45)
I have thought long and hard about switching to the XDm with thumb safety (only in some 9mm models i understand), but I don't want to downgrade to 9mm because i subscribe to the "carry the largest caliber you can comfortably shoot" school of thought.
If you're comfortable carrying one in the pipe w/o a thumb safety then by all means do it. I'm not comfortable with that, but that's just my comfort zone.