I have one but it is on one of my Sigs. I love it and don't see why you couldn't use it on an M4. The thing is built like a tank and has three different mounting heights. I have mine on the intermediate height and a Larue QD mount. The lowest one would work well on the M4. The IR is awesome and even when it is off you can see the reticle very well, even in low light. It's nice not to be tied to batteries. I would post pics but the damn forum won't let me post links or anything due to my low post count.