On my second filter sent free from Katadyn because the first nearly stopped flowing.  Now the same for new second filter.  The flow is fantastic out of the box.  But within in a few days on the trail you will begin to notice it takes a little bit more squeeze pressure to get a drink.  Both 100 mile section hikes, one in VA and the other in VT, by day six it was almost down to a trickle.  In order to get the filter back to near full function it needs to be soaked in either a vinegar water solution overnight or demilitarized water.  Not convenient if thru hiking.  Not to bad for a section hiker. Great concept, poor execution.