Don't waste your money with GRs on a pistol. They are great for rifles and shotguns equipped with a stock, but nothing more than a marketing gimmick on a pistol.
The reason XS Big Dots are so quick is the enormous front sight paired with a low profile, low rise V-notch on the rear. You don't lose the front sight behind any of the rear sight if your grip or firing stance is impaired. If you can't see the front sight, it's because you have the gun angled too far downward. With traditional sights, it's easy to lose the front sight behind either side of the raised rear sight areas, or behind the middle of the rear sight, hence making them slower to put on target than XS Big Dots. With a ghost ring setup, you increase your chances of losing the front dot behind any part of the ring (a 360 degree area). GRs are very effective when paired with a stock and a proper cheek weld, but handguns do not offer the sight alignment consistency of a long gun; thus, they should not be equipped with ghost rings.
I shot a G19 with the Arotek GRs and it was a complete joke. From a draw, I consistently lost the front sight if I did not have the gun perfectly lined up. Something else to keep in mind is that on a long gun, the rear sight (ring aperture) is situated fairly close to your eye, making it bigger and giving a larger area for the front sight to reside in. With a full arm extension, it's at least 14-16 inches away from your face, making the area inside the aperture tiny.
If you want fast target aquisition, go with XS. If you want match grade accuracy, go with target sights (like rifle sights, they are more accurate than GRs). Simply put, GRs do not belong on a pistol.
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