Plus a two way street, eliminating a target also affords the target something to shoot at. I was taught, gun in one hand and light in the other and away from the body, as another alternative.A Maglite and the Harries technique (or several others). That also spares you the risk of using a gun as a flashlight... and the cost of the adapter kit.
Gun lights are great tools, for the right purposes. But I'm not exactly convinced they're ideal for home defense; you want to be able to look at things in the dark without pointing a gun at them.