OK, first of all I know I'm going a little out of the core subject here but as a FNG I thought I'd share another view. While they are not the same type of sights being discussed here since they are basically not for shoulder-fired weapons, ALL of my carry guns have Crimson Trace Lasergrips on them for a couple of reasons. First, I'm getting a bit older and starting to have a little trouble seeing some things as clearly as I used to. Second, in a defense situation, just the sight of the red dot may give the bad guy a little pause or possibly even cause him to change his mind.
I do practice with them so that I can place the hole where the red dot is consistently and quickly. Especially in a limited light situation, I can't think of a better way of hitting my target. It's also possible to use them in a situation where your gun is not right in front of your face so the other guy can't use that as an aiming point for a head shot.
Just my 2 cents worth, but I have them on my Ruger P89 9mm & P90 .45, my Charter Arms Mag Pug .357 and my Taurus 85 .38 Special. So no matter what I am carrying (mostly the P89, but occasionally the Mag Pug or the P90), I think I have a little better advantage than I would have with only iron sights.