Rating: 3 / 5
BD Cosmo purchased in fall '06 is pretty much what i've come to expect from Black Diamond.
Quality. Nice packaging (not the box, by this i mean the headlamp itself). Reliable. Functions well. Money is not wasted.
However, there's really nothing to make the Cosmo stand out compared to its main competitors from Princeton Tec and Petzl.
The Cosmo uses a 4x5mm LED array and is powered by the fairly standard, for this type of headlamp, 3xAAA batteries. A single switch controls the headlamp's operation. A full depression of the switch (which produces a distinctive "clicking" sound) turns the headlamp ON and OFF. The switch also provides good tactile feedback and is large enough to operate with gloves as long as the gloves aren't too thick, in which case it becomes a bit more difficult.
When OFF, fully depressing and releasing the swith turns the headlamp on in HI output mode. When ON, partial, inaudible depressions of the switch cycles the headlamp to MED output, LO output, FLASHING Hi output, and then back to steady HI output.
When ON, fully depressing and releasing the button turns the headlamp OFF regardless of the mode that it is operating in.
Light output using the fresh Mfr supplied batts is on par with a pre-'06 ZipkaPlus. I couldn't tell the difference in brightness between the two. However, the PT Quad that i have is much brighter. Also, an '06 3LED Zipka and an '06 4LED ZipkaPlus are BOTH MUCH brighter than the the Cosmo.
Have used the Cosmo long enough to make any determination as to battery life. In my experience with a fair number of BD headlamps (going all the way back to the original 1LED Gemini hybrid headlamp), i will be pleasantly surprised if the "burn" times live up to BD's claims - at least down to what i personally consider a minimum amount of light output. But the jury is still out on this verdict, so take my cautious skepticism with a grain of salt.
I give the Cosmo a '3' since it's about average. IMO, you won't have wasted your money if you buy one, but there are much better options out there, IMO, from both Princeton Tec and Petzl (viz. the PT Quad, & the Petzl Zipka/ZipkaPlus and it's nearly identical sisters).