[pct-l] steripen for water purification

[Laura Fox]

Hi ... I'm sure somebody here must know the answer to this.  So I was reading
about this steri-pen device that zaps your water and kills everything and
weighs about 4 oz and lasts practically forever.  Other than the fact that it's
expensive ($100?), what's the catch?  Why isn't everybody using these things? 
I'm still planning to go with aquamira or bleach, but I wonder whether this
device would be a good idea.  I mean, the price isn't too much more than I
would pay buying a bunch of bottles of aquamira and mailing them to myself.