I have one I've taken on maybe ten 2-day trips. The flow has reduced quite a bit even though I'm not aware of running any particularly dirty water (put intended). This last trip it was very slow, I had to backflush every other litre to get anything out of it at all. I'll probably pick up a Saywer Squeeze before my next trip in a few weeks but am stubbornly trying to clear it with hot water and vinegar soaks just to see if it's possible. If I do give up on it I might cut it open to see what's inside and if any obstructions are visible.