Laser Use
Laser sights are particularly useful in low-light situations, where using the conventional sights may be difficult. By casting a red beam to your target, you are free to concentrate on the situation. The potential disadvantage of using a laser sight is that, while it readily identifies your target, it also identifies where you are, which could be a disadvantage if you are trying to conceal your position.
Laser Colors
Laser sights are generally available in red or green. Red lasers are usually less expensive than green lasers and are very popular among civilian shooters. The disadvantage of red lasers is that they perform very poorly in bright light and are nearly impossible to see in daylight. Green lasers perform much better in brighter conditions and are the choice of many law enforcement agencies.
Laser Mounting
A laser sight can be mounted on a shotgun in a variety of ways. Perhaps the most common method is with the bracket that attaches directly to the end of your shotgun's tubular magazine. Rail mounts are also very popular and allow your laser, or other accessories, to be mounted wherever you choose; rail mounts are also commonly used for mounting scopes on shotguns.
Intimidation Factor
Perhaps the greatest advantage of using a laser, at least in a self-defense scenario, is more psychological than tactical. The appearance of a red or green point of light indicating the spot that your shotgun is aimed on the would-be bad guys body can be extremely intimidating. This intimidating device can potentially dissuade aggressors from continuing and possibly defuse a dangerous situation.