Every review I've read basically says they aren't all that good. The large dot makes it difficult to be accurate at longer distances. Not to say that you can't be accurate with them but you will be as accurate faster with other sights. The only real application I've seen people recommend them for is people with ailing eye sight or for people that don't want to or can't practice a lot
I like them. They are for CCW guns and duty guns. If you're practicing shooting at targets more than 10-20 feet away for CCW, then you're doing it wrong.
the XS site is about fast target acquisition at CCW ranges. It's not for target shooting.
Anyone, short of a navy seal, who thinks they're going to have a chance to think and actually use traditional 3-dot sights, or even night sights, in a surprise CCW encounter is fooling themselves.
Now, you don't have to listen to me. I haven't been in a gunfight. But this guy has... several (14)... and he swears by them:
I put the XS Big Dot on my XDM and I really like it. I practice a lot the stuff on here and I really notice the difference on the FAST, the Bill Drill, and the press drills like Press Six and Acceleration. The sights are good enough to hit COM at 15 yards consistently and I'm OK with that for defensive purposes. Keep in mind, I've never shot at anyone or been shot at, so I can't offer any trial-by-fire insight... just my experience shooting at paper and a few thought experiments.
Have them on my Glock 27. Personally they help me a tremendous amount (in time to first shot and second shot split).
I do not see any disadvantage shooting them at distance either. They take a little getting used to but that is all (putting the dot on the target). When I got my carry conceal permit in Kentucky. I tested these (for almost 3 months) side by side with/ against Warren Sights and Novak sights (both excellent sights) on a Glock 19 and I consistently did better with the XS/24 on the Glock 27.
While not a competitive shooter I have shot them in competition and did not feel handicapped.
IMHO opinion it is because they act like a peep sight where you are only focused on the front sight (which is easier to pick up) and the rear sight less of an issue because your eye self aligns it (for the most part). I hope that makes sense.