Well I posted a lengthy reply, but it got lost in the 3am update!
Short version-I have both the Streamlight mentioned and an older Insight X2-they now have an LED version of the X2, so assuming the light output of both is equal (and they're rated the same), I think I'd check into the X2 LED before buying.
The X2 is smaller, but the biggie is I like the attachment system better than the Streamlight's hybrid (pushbutton with screw). The X2 is just a snap-on affair-you can pre-adjust the Streamlight screw so it should just snap on, but it's not very confidence inspiring unless you tighten the screw. 'Course, you know what's going to happen if you tote it around with the screw pre-adjusted-when time comes to whip it on the gun, the screw will have moved and it either won't fit (and you'll be fumblin'/mumblin') or when you let go thinking it's attached, it'll end up on the ground! :banghead:
I have the old incandescent X2-better mounting system and smaller light, but the incandescent light is pretty pitiful and has the worst yellow tint of 'bout any light I've seen.
They make a $30 upgrade for my old X2, but Insight LED stuff is hard to come by as it hasn't been on the market very long.