I just got the TK10 in the mail last night. First off - NO problems with a loose head.
Regarding gun mounting, I don't have a caliper to check the exact diameter of the TK10, but the barrel seems a bit thick (maybe 1.25"?). I think most gun (rifle) mounts are for lights with barrels in the ~1" range, but I know Command Arms Accessories makes a few for various barrel diameters (I just don't know if the diameter of the TK10 is within thier range). Other than that, it seems sturdy enough to handle the abuse, but I'd want to play with it outdoors to get a better sense of the beam characteristics before putting it on a rifle. BTW, I think that the TK10 might be a bit large to use in a cigar hold with a handgun, but I don't have very large hands. Just my $.02.
Edit - I'd also assume some may be looking for a tape switch for the TK10, which I don't know about, but the pics on the FenixLight.com website do appear to show the TK10 mounted on a rifle or SMG.