They are good sights have a couple on long guns. On handguns however they can be in the way when seconds count. And for me, I have many thousands of rounds through a handgun before red-dots existed, and have hundreds of hours of muscle memory and sight-picture development to overcome by placing something between my eye and the target. if you spend a year getting used to that red-dot and then remove it, or use someone else's weapon that doesn't have one you'll have that training to overcome before you're as effective. in a crisis, that might be the difference between going home or not.
That was brought home to me a couple of years ago, one of the guys the frequent our range had been using a red-dot for a year, and wanted to try one of our Sig P226 variants. It had standard OOTB sights, no red-dot, and it took him two mags of ammo to get on target. At first he blamed the gun, then one of our instructors put six on the "X" and declared it was NOT the gun. The guy was an excellent shooter over stock sights for years before buying a red-dot, but over the year he had re-trained is sight-picture expectations and his muscle memory to react to the red-dot, and going back required an adjustment. Imagine getting in a gunfight and the battery goes dead ...... bad time to be forced into that adjustment.
