As for function and use of this light, it was not intended for me to use as a replacement to any other light, but did work well for small tasks like finding keys, looking for objects in the dark on the ground, and fumbling for gear in the truck. I was not expecting this light to be as bright but it's [advertised] 4 lumens worked well. I was able to read a small pressure gauge from inside the truck at about 5 yards away.
The body is advertised to be made of solid brass but other than weight appears to be made of aluminum. Its probably just under 1.5" long and about 5/16" diameter. It is advertised as water resistant but I would probably call it waterproof. I dropped it in a water tank and it stayed for probably 15 minutes while I decided how to get it out without freezing my hands. Still worked fine until lost.
The TRUE Utilities "Smallest light in the world" was pretty handy, but I'm still considering if I will get another.