I bought one and found it to be useless. It is a pinpoint accurate device being used in an area-impact weapon, and the sighting system on most shotguns isn't precise enough to make use of the laser dot on the target. Save your money. I use mine to tease my cat.
I'd be using it for a 23" cantilever slug barrel with a 3x7 scope. Was hoping to limit the number of sabot slugs I have to use to sight in.
Most of the good shooters, do it the old fashioned way.