I've got one, my wife bought it for me for fathers day a year ago. Works well, at least I've never gotten sick. It's small, light, easy to carry, and makes your good water taste like it's been chlorinated. That said, it will kill viruses and cryptosporium and all the nasties that a filter might miss. The taste lessens with time and it's not horrible, but it's not all that great either.

On a side note i saw a UV light that goes into a Nalgene bottle and is supposed to be as effective. I'm tempted to try that one.

jm2bits