John O.wrote a review of MSR HyperFlow Microfilter on May 23, 2012
If you're looking for something to use one weekend a year for one person, you're in luck. If you plan to use this more than once in a blue moon, forget it.
I bought this last year while hiking the Appalachian Trail. It pumped Great for the first day or 3, filtering about 3 to 4 Liters of water, once a day.
By the end of the 6th day, it was Very difficiult to use. By the end of day 9, it was straight up trash! It is impossible to backwash!
MAYBE you can backwash it if you saved the stupid Nalgene adapter & actually carry a heavy Nalgene bottle (sorry, 99% of thru-hikers drop these way before the 1/2 way point).
I wouldn't recommend this to anyone.