The Safariland ALS is GREAT for an open carry holster. I think its a "SERPA" killer. The thumb button is VERY natural when getting a positive grip on the gun before you draw. Unfortunately you really want that rock motion and this doesn't have it.
IMO, in a SHTF OMG I NEED TO DRAW AND SHOOT SITUATION - I feel that it would be easy for your brain to forget that rocking motion and after gripping the gun and hitting the button (you can't NOT hit it if you grab your gun) you may find yourself left tugging on a holstered gun.
^this is purely MY opinion and if you feel training and drawing A LOT will program it into muscle memory, well then - you go girl.