Stoven!stoven said:Personally, for light output I would go with the regular Ultra.
The Ultra M is beefed up version for the military. The M version has a lens(I think 2 actually) in front of the LED to help with sealing and it has double O-rings. Since the M has lenses it blocks a lot of the light output making it worse than the original Ultra.
Since the regular Ultra has an exposed 5mm LED there is no loss of light output.