User Review: SteriPEN Classic
Price Paid: $149
Have used mine for the last two years and haven't gotten sick once.
Good points are that it's smaller than most water filters and as far as I know is completely effective against all waterborne bugs. Easy and quick to use. Water is without chemical taste (though since it isn't filtered, it will retain the taste of the stream or pond it comes from). Reasonably lightweight, though far heavier than say, MicroPur tabs.
Bad points. Expensive to buy. Annoying child-safety button pushing code to operate. More important, the lamp loses effectiveness after 625 gallons and must be replaced, and the lamp makes up most of the cost of the unit. Add in the cost of 4 AA batteries that must be replaced regularly and it is the most expensive of all backcountry water treatment solutions.
UV light, unlike chem treatment, has no continuous effect to prevent regrowth of bacteria, and so UV water must be consumed reasonably quickly or else re-treated. Fragile. Can break if dropped on something hard. Replace the protective tip and place in case immediately after use.
Finally, since UV treatment does not work as well on turbid water, and since sediment-filled water can make you sick (diarrhea) as well, you will need some method (sock/sand, coffee filter) of straining turbid/muddy water or else wait for it to settle out.