There is no water filter that can compare to this model Katadyn. I have used the predecessor model of this one since 1969, just replaced filters a few times. It is the only truly field-serviceable model available, and tests better versus the specs than anything else in actual field conditions. Don't waste money on other filters that break, lose their power over time, or go out of style. The engineering changes on this one are great...mushroom handle, clip, better spout and bottom, scotchBrite versus brush, etc. Otherwise, the guts are the same for decades, and for good reason...nothing comes close. I've used it on trips of 22 days in Bangladesh 42 days in the LaConde Jungle, 65 days in the Peten, and 120 days in Hondouras, plus over a thousand nights in the Rockies with no trouble. Mud puddles come clean. I use the Katadyn everywhere but the rare times when I need a true purifier, such as when in the polluted Khlongs (read: sewers) of Southern Thailand, where Hep A,B,and C are present, necessitating a true purifier. Then I am forced to go to General Ecology's First Need (don't know why BC does not carry these!).
One review cited problems with it retaining water...if you pump it four times in the air after you're finished filtering, it clears fully. It maintains its flow rate if you clean it better than any other. A backpacking essential, a world-travel essential, well worth the money.