My opinion is that they're unnesessary. I find it a little hard to believe that a threat would be deterred by noticing a little red dot on their shirt, and not by looking down the gun's muzzle. I haven't heard of any cases where a BG was being covered by a weapon and yet continued to pose a threat, but upon turning on a laser, they decided to surrender. I think that if there were instances where a BG surrenders due to seeing a laser, its probably because they're noticing the gun more so than the laser. I think that in this case, these guys would have surrendered at the presence of a gun, laser or no laser.
I've owned crimsontrace grips before and I do think they are a high quality product. They work as advertised, without a doubt. I don't think they are any help in a gun fight, however. Most gunfights are within 7 yards, with a huge majority of these being inside of 6'. At these distances if your looking for a dot on the BG to fire your shot, your going way too slow. Same goes for trying to aquire the 'classic sight picture.' At these distances, its all about point shooting, flash sight picture, or indexed shooting. Anything else is a waste of time. Even in low light I don't find lasers to be an advantage. I know, personally from training that I can bring my gun up into my line of sight, without really focusing on the sights, and make accurate shots out to 15 yards. This is much faster than trying find a 1/4" dot on a moving adversary, while your moving (because if your shooting, you'll both most likely be moving). Even shooting with the laser from the hip is still going to be slower than indexed shooting, because your having to locate the dot on a dynamic target.
One argument thats always made about laser sights is that they allow you to shoot from one side of cover and observe from the other side. I understand this argument, but often in gun fights, cover is not even utilized. Im a civillian, so any of my deadly force encounters are going to be reactionary. That means that I'll be reacting to an adversaries threat, and hopefully doing the right things to reset his plan and make him have to observe my actions and get him into a reactionary state (as the OODA loop explains). If cover is immediately available I'll take it, but often times its not and trying to hunt for it and move to it, will keep me in the observe / orient stages of the cycle. In the dark, trying to find / move to cover creates a host of problems, especially in an unfamiliar area. The point being, cover is sometimes overrated and we may be better served just by rapidly moving off the X and shooting fast and hard. Laser sights don't offer any advantage to that end, in my opinion. As a friend of mine has said, There comes a time when we should stop buying all the bells and whistles and just invest in ammo and training.