I have used them for several years now. I live /hunt in the Colorado Mountains . They work great . In the winter , it is really the only way to go . The filter element in a pump will freeze in cold weather, yet when you pump it , it will still pass water, this is because the pump bypasses the filter when frozen and just pumps contaminated water out .I would suggest getting the "classic" model that is run with AA batteries and also standardizing the use of AA batts with everything that you carry in your pack GPS, lights , head lamp, steri-pen . This way you can switch good batteries from one unit to another if needed during an emergency .