I recently purchased the shield with a safety. My logic: utilize safety when holstering and unholstering. Once holstered, safety is off. Normal (casual/daily) unholstering, safety is engaged prior to.
Train with blue gun (3 draws) morning and night w/o safety being "swept" or disengaged. So when I'm holstered, it's hot and in the highly unlikely event I ever need to draw, I'm ready.
In summary - in all normal instances the safety is on when the weapon is out of the holster and off once safely holstered.