I have XS Big Dots on a G19 and a 640-1. Great for quick target acquisiton at close range. The G19 is the only one that, at present, also has an XS rear.
I also have a standard XS standard for my LCR which is zeroed nicely in the rear notch. The Big dot would work fine, also, but precision is lost beyond real close range.
I've replaced a number of sights with the XS STANDARD sight, which I've come to prefer. Still big enough to pick up quickly and small enough for some fair precision.
I do not, however, prefer the XS rear sight. I prefer the standard square notch. Since the front sight on most pistols is very high, it requires a higher rear sight to compensate.
My P228 SIG zeros perfectly with the XS standard dot and #10 rear. I've ordered two more rear sights from Sigarms and two XS standard sights so I'll be converting a couple more SIGS. They're fast on target.
The change is prompted by my eyesight which isn't, in my 6th decade, as good as it used to be. If it was, I'd probably stick with standard sights, but would have no problem with XS sights, either.
My Colt Commander zeros well with the XS standard with no replacement of the Novak rear necessary. It tends to work that way on some 1911's--but not others.
My Springfield Champ. zeros with the center tritium even with the white dots of the rear sight, which leaves about half the dot above the notch. Shooting with part of the dot out of the notch is an easy learning curve.
NOTE: I've been guilty of referring to all XS sights as BIG DOTS. It's important to remember that there're BIG DOT and STANDARD. I believe the standard will work quite well for most of us.