Pump filters have the one advantage that you can lower the intake nozzle into some small spaces where you could never fit the mouth of a filter bag (think small trickle of water in a rock field). They're also good for situations where one has to filter a large quantity of water with no place to hang a gravity filter. Finally, there are pump filters that will remove a wider range of pathogens (like viruses) than the squeeze bags or gravity filters, but not many people travel in places where this is necessary. In short, the pump filters have been rendered nearly obsolete by gravity filters and squeeze bags. My Katadyn Hike Pro and my KatadynGuide filers are gathering dust, while my Katadyn BeFree squeeze bag has become the equipment of choice on backcountry outings.