I actually have a Pak-Lite, it is a little cap you put on a rectangular 9v battery... it is miniscule and does 600 hours on low... amazing functionality. I think it may be the ultimate in light and functional.
Interesting. I can see where it might work well for some.
It isn't particularly small or light when you include the battery, so unless you need that kind of battery life it might be over kill. My little eGear Pico claims 17 hours of battery life and that is enough for me to tour a very long time since I typically use it only a few seconds at a time. The same batteries lasted me for a coast to coast trip, a week long tour, and a couple week of backpacking.
Those who use their lights a lot will probably not like the Pico because of limited battery life (17 hours). For them the 600 hours of the Pak Lite may be just the ticket. It would allow long hours or reading in the tent.
Me, I could probably cross the country 20 or more times on 600 hours of battery so I see no reason to carry a 1.6 ounce battery. For me, the Pico seems to be just about the right battery life (17 hours), weight (0.2 oz including batteries), price ($10), and convenience (it is on a cord around my neck).
I really like having it on a lanyard. When I used a headlamp it was never handy when I needed it, so usually I just did without. With the Pico I have that 5-10 seconds of light that I need right at my fingertips. With other lights I have used, when I need 5-10 seconds of light I'd need to spend 2-3 minutes finding the light, so I usually didn't bother.