I use these as a more cost effective replacement for the katadyn befree filter cap. It doesn't fit out of the box - you need to trim a couple of mm off the bottom of the gray collar, otherwise it doesn't screw down tight on the befree soft flask, and possibly not on the cnoc bag either. I actually prefer these to the befree as the top cap is more secure for the times you need to use the soft flask to carry extra water. Otherwise, I've not observed any difference in performance. I've just got back from the 800 mile AZT with some of the most gross water sources immaginable, and a single one of these got me through the entire trail - water flow was a bit slow towards the end, but still usable.