visible laser is good for LOW light. If your LE and you take a shot with a visible laser in the dark your going to be squirming when your asked how you ID ed the dead guy in the dark - (did you see his hands?)
white light does have a distinct disadvantage for the guy with the light that was alluded to before - for that spit second they have you before you ID them.
and NO it isnt an automatic shot when your light goes on - there is still the ID whether friend or foe before the shot. Bad habit to train without an ID.
having said that think about where your sights are if your up and ready for the shot.... your threat (the hands) may very well be in the area occluded by your site picture. This means different things if your in the corner of your room listening to an intruder coming down the hall towards your door or if your a cop doing a no knock on a crack house.
If you get gun "furniture" as the Brits like to call it. know how and when to use it. Dont get it because its cool. (or your cat really reallly really likes that red laser dot game). Have a plan for how your going to "deploy the toy"