Hey Leif!
First, I'm not sure if you've found
this review, but it's an amazing pictorial comparison review between the Kroma (non Mil-Spec) and the U2... it really should tell/show you everything you need to know!
That being said, you should be able to easily see that the U2 has better throw and sidespill than the Kroma... if you are using it for just a white light, then it's what you want... although if you're using it for Red as well, and thinking about carrying a red filter around, I think you might consider the Kroma Mil-Spec (or a SF A2?)
I think that comparing the Kroma (Mil-Spec or other) and U2 makes sense to a certain extent, however they're pretty different - with the U2 giving six levels of white light, and the Kroma giving 2 levels of white, red, and blue, or a mixture of white with either red or blue. (The Milspec adding IR and yellow-green).
If you just want a white light - go Kroma - it's no question. If you want just red in addition to white - I would say the filter would be a possibility, however it's something you have to worry about carrying around. But the Kroma is certainly a good middle-ground if you don't want to carry a filter around... as far as brightness goes - although it doesn't throw as much as the U2, it'll still get most of the same jobs done IMHO. If you want more than white & red - no choice - go Kroma or Kroma Mil-Spec.
john