Here is one review I saw:
SPECS
Manufacturer: Hydro-Photon, Inc.
Manufacturer's Website: SteriPEN
MSRP: US$99.95
Listed Weight: 3.7 oz (105 g)
Measured Weight: 3.5 oz (99 g)
Measured Weight With included carrying case and set of 4 Energizer lithium batteries: 7.25 oz (206 g)
Listed Weight at 6.5 - 8 oz (184 - 227 g) with batteries depending on type of batteries.
Listed Dimensions: 7.6 in (19.3 cm) L by 1.5 in (3.81 cm) H by 1.5 in (3.81 cm) W
Requirements: 4 disposable or externally rechargeable AA batteries
Listed weight at 6.5 - 8 oz (184 - 227 g) with batteries depending on type of batteries.
NUMBER OF EXPECTED USES (info obtained from manufacturer)
AA Battery Type 16 oz. of water
Lithium Disposables (Photo-type) 180
*NiMH (Nickel Metal Hydride) 180
**Alkaline 20-40
**NiCad (Nickel Cadmium) 10-20
*Recommended choice for cold weather use
**Not recommended for use in the SteriPEN
Manufacturer's Description: SteriPEN purifies water using ultraviolet (UV) light. Whether your source is a clear running brook or a hotel tap, SteriPEN destroys viruses, bacteria and protozoaincluding Giardia and Cryptosporidium in seconds. SteriPEN suggested retail price: $99.95.
PRODUCT DESCRIPTION
My SteriPEN came in a blister pack which included instructions in several languages and a nylon carrying case with a hook and loop fastener closure. The light tube is covered with a protective blue cap. The SteriPEN operates on 4 AA batteries (not included). Batteries were easily installed by rotating the cap on the end of the unit. String can be add by a small hole at the base of the unit (not included). The unit is made mostly of plastic with a glass light tube. SteriPEN is easy to use with a single button for operation. One green LED indicates a successful use, while a red LED indicates an unsuccessful use. The button is pressed once for purification of 16 oz (.5 L) and pressed twice for 32 oz (1 L). The unit works using ultraviolet light which is invisible to the human eye. To indicate the unit is operating, there is another light in the tube which can be seen.
FIELD USE
I used SteriPEN as my primary means of water purification for both me and my wife during our 2006 thru hike of the Appalachian Trail. I hiked the Trail during all four seasons allowing me to use my SteriPEN in temperatures ranging from 12 degrees F (-11 C) to 105 degrees F (40.5 C). The directions state that the SteriPEN should not be used under 32 F (0 C), but it was not clear if the instructions were referring to air temperature, or water temperature. Obviously, it would not work if the water was frozen, but it did seem to work fine when the outside temperature fell below freezing.
I loved the SteriPEN's light weight. Mine weighs in at 7.5 oz (212 g) including the carrying case, 4 Energizer lithium batteries, and a string that I attached to use as a lanyard during operation.
I started the AT with the SteriPEN and due to a malfunction, I traded the SteriPEN out at approximately 250 miles (400 km). At approxiimately 500 miles (800 km), I was experiencing the same problem with the second pen. I contacted the manufacturer again and was offered another exchange. Both exchanges were offered at no cost to me. Through my own field tests, I was able to work around the malfunction allowing the third SteriPEN to survive the remaining 1500+ miles (2500+ km).
When the unit started to malfunction, the manufacturer gave superior service. It was "no questions asked" when I talked to them on the phone...except to find out what was wrong with the unit and to find out which particular model that I had. They sent a replacement unit to me immediately without asking for credit card, payment, or immediate return of the malfunctioning unit. When the new unit arrived, there was a return mailing label included. There was no cost to me for the exchange. They also offered to get back in contact regarding the malfunction after conducting some tests. I did not take advantage of the call back offer.
As I have mentioned, there was a malfunction on all three of the units that I used. As a result of long duration of use, I was able to pinpoint the problem. Extended time periods in the field would "confuse" the SteriPEN. I would get to my campsite, prepare to use the SteriPEN, push the button, and the red indicator light would illuminate immediately, indicating that there was a malfunction. I was able to determine that the extended outdoor use seemed to create too much humidity within the unit and caused this malfunction. The malfunction occurred with a much greater frequency during periods of extremely high humidity and periods of extended rain. I was able to "fool" the unit when I got a red light by waiting for the indicator light to stop blinking and then placing the unit in the water, just as if I were purifying the water. Then I would pull it out of the water, just as if I had completed the purification, then push the button again. The SteriPEN would then work just fine for any number of uses. I am certain that this would not even be an issue to anyone using the SteriPEN for weekend or week long treks. The problem also goes away after the unit is in a controlled environment (inside) for approximately 1-3 days to get a chance to get completely dried out.
Throughout the hike, I used the SteriPEN with many types of water sources including creeks, steams, rivers, lakes, ponds, springs, and more. The instructions warn against using the SteriPEN in water that is not clear. Some of the water sources that I had to use were very questionable due to smell and clearness. Neither I nor my wife had any adverse health problems during the entire hike, making me feel confident about using the SteriPEN.
Immediate gratification is the best feature of the SteriPEN. It only takes about a minute and a half to purify a quart / liter of water with little to no effort. Just stir the water occasionally. With no chemicals or filtration, the water I purified from the mountain springs is the best that I have ever tasted.
Durability was good. I dropped my SteriPEN countless times from waist height. It landed on rocks, rolled down hills, and floated down rivers many times. That is why I eventually started using the lanyard. I never had a problem due to impact or total immersion in water. In conversations with the company, we were told that they put the SteriPEN through many tests for impact and water resistance including hosing it down with a power washer.
I used the SteriPEN to purify an average of about 8 - 10 quarts / liters per day. A set of 4 AA Energizer lithium batteries lasted between 20 (during colder time periods) and 30 (during warmer time periods) days. I also used Energizer Titanium batteries which seemed to last for a relatively equal duration. I did not use standard alkaline batteries nor rechargeable batteries for a long enough duration to make any recommendations.
THINGS I LIKE
Light weight
Durability
Fast purification time
Superior service from the manufacturer
THINGS I DON'T LIKE
Malfunction of the unit under extreme use.
