In reply to lachy773: I had the katadyn bottle. Worked well and was convenient.
The only problem was you never really knew if it was working. I mean there was no indication of if it was still working or not and you had to count the number of liters it had been used for.
I was confident with it at first but after a month or so began to wonder.
Switched to iodine drops after that. Much better as you know they are working and can be used in any bottle. Much cheaper as well I reckon. Now, and for the alps, I'd just go with chlorine dioxide tablets and a piece muslin wrapped around your bottle with an elastic band for keeping big bits out when filling.