I looked a bit but didn't find any detailed specs on this product yet. The team that created it has some pretty impressive credentials.

I think there are some advantages here. The main one being that you can bring fuel cartridges to resupply the charger and each one is equivalent to 12 batteries.

I'm not sure the device would be heavier than a dozen batteries either, which is probably closer to a fair comparison, and if you add one fuel cartridge it's the equivalent to two dozen batteries, and so on. So, if you want to do some intensive use of whatever devices you have this may be a great solution.

It might also double as a hand warmer

I've been looking into the "Raspberry Pi" and GPS, compass, weather and other modules that can be hooked up to it so I can make my own custom handheld devices. In the process of doing that I've come across some other ideas.

A GPS that does nothing but track your path might be made very lightweight with a very low power consumption, and probably pretty cheap too. Check these out:

GPS Recievers

If you hooked one of these up to a tiny breakout board with just the componants to record the data to a SD card you could probably get it weighing in at just a few ounces with rechargeable batteries that would last for days. I know there are small devices that do this, but I'm thinking of something that you can attach to the top of your pack and forget about until you get back.

That compass module at that site is pretty neat, and they have some other cool gizmos there too. I'm going to start playing with some of that stuff, I just can't resist it