I recently purchased a G19. I installed the XS standard dot sights. Installation was easy. Front sight...very snug fit (which is good) and no play that I noticed. Installed with red loctite.
Rear sight installation was easy too. However I borrowed a laser bore sighter that helped with the alignment. The instructions state you may have to file to fit. However I did not have to do any filing. It fit well right out of the package. Installed with red loctite per the instructions--IMPORTANT, read the instructions - e.g., you don't use the red loctite on the set screws.
I visited the range with my oldest daughter (16 yr old) to test out the sights. I shoot competitively and was initially very frustrated. My shots were low and slightly to the left. When I shot with the gun resting on a brace, I was just low and center. Then I remembered that these are combat sights...which I knew when I bought them. The reason that I was low is because that's where I was aiming. Being slightly left was a matter of 'dotting the i' and ensuring that the front sight is centered over the vertical rear sight. It takes some getting used to. I made the adjustments and it was fine.
As I say, sight alignment takes some getting used to for me. I would repeatedly fall back into shooting low. I also found that because I am so accustomed to other more standard sights, it would take me longer to acquire the target. However this issue is simply due to me...not the sights. I simply need to learn to use them better.
Amusingly, my daughter seemed to pick them right up. In no time, she was putting all rounds on target as fast as she could pull the trigger.
In all, I like the sights. For those that have shot for a long time, these sights may take some getting used to. While I have read others saying 'these are not for competition', I mainly compete to get better at shooting what I carry. So I don't see issues with shooting matches with these sights. I expect I will not place well with them for a bit. But competition is a good way to learn quickly.
One negative that will not be overcome by practice is that even the standard dot covers smaller targets. For example, shooting a small steel plate will be challenging since you will likely not even see the plate.
Positives include - easy to install, very easy to see in the dark or low light conditions, and with practice, I expect I will eventually be able to acquire the target faster than the standard Glock sights.
Just my $0.02 worth. I hope it helps for others considering these sights.