Just make sure it's good and reliable. I run the X300 on a pistol and it's great. One could also run a Scout light setup for a similiar cost.
(Weapon mounted scout lights go for almost half of retail on eBay, too bad the rest of their models don't tend to go for that low)
Surefire? I thought I could make that out. I've seen their shotgun versions and was really impressed with how nicely its made and easy to use. I've still got to post my inforce light and cheapo laser mount.
I was actually really surprised to find out that it fit perfectly with just the Magpul pica tinny rail. Yeah, it's a Surefire M900A. And yeah it's pretty dang heavy, that's why I didn't put it any farther forward.
This is the inforce 9v. I added the pressure switch separately which turns on whichever color led I previously set. Green, white, red, and blue. Just a turn or the thumb screw and I can take the light off. The way the light mounts I was able to mount a cheap laser on the magpul rail.