"Great Tracer Unit, but beware, you may not get an JG unit. I received an off brand unit, but pretty much as it was described. Works great, I have it on my G&G GR16 and works like a charm. The package came with 4 AAA batteries which was nice of them. You unscrew the bottom (where it threads to the barrel) to be able to insert your batteries. I like the concept, but because your screwing in cw, and unscrewing ccw, your ending up having to hold that tiny part to try and screw it onto your gun. Otherwise you'll end up unscrewing the battery compartment trying to screw it in the gun, I found that a hassle. They should have at least done it half way up to allow for better gripping."