All my duty type or CCW are single dot front.
Cheaper to buy only one tritium vial (if going night sight)
my eyes can line up a single dot in a notch faster
in a close combat situation, not going to have time to line up sights.
my focus is more on the front sight (instead of two other dots)
For years I carried a Glock 3 dot sight on duty and off duty was a Colt Officers ACP with a single dot front and a King Tappen rear which is just a white bar under the notch. the speed in which to get my officer's on target and shooting was much faster.
I took a single piece of 1/8" white pin stripe and placed it just below the rear sight notch and it improved my shot time. in fact I blackened out the rear tritium dots
my current set up
DW CCO tritium front black 10-8 140" rear
Springfield Armory MC OP factory front tritium black 10-8 140" rear
Custom Colt 5" tritium front, black Heinie rear
Colt Officers ACP front dot King Tappen Rear (no longer made)
Glock 17 10-8 brass dot front and black 140 rear
Glock 19 Trijicon 3 dot night sight with the rear dots black sharpied out
SWCS9D front dot, black novak rear
Glock 34 front dot, blacked out white bar rear
MP9 front dot, blacked out rear dots
when and if I ever get a Shield Nina it will have the rear dots blacked out or switch to a 10-8 rear sight.
the green nail polish front sight is my duty 5" Springer. I always ran a .125" rear notch for best accuracy. my eyes were getting up in age and for sometime I fought with myself to go bigger rear notch to speed up my first shot. My Glock first shot was much quicker last year than with my duty carry. It was making me frustrated until I realized the rear notch on a Glock is huge compared to .125". I switched to a .140" rear notch and used some of the wife's nail polish to grab my attention should I need to make a hasty shot and I can at least get that quick green flash. My first shot speed returned and me happy. Did I mention I like a single dot front?
here is how I ran my CQB from 98-2005 (I never saw the rear bar unless night time)