I've used these filters (I have 2) for 7 years taking groups of 9 to the BWCAW. The key to success is to use a pre-filter such as the silt-stopper, and clean the element frequently. If this isn't done, pumping becomes hard quickly and the piston can break rendering the pump useless. MSR does replace them under warranty without question however. With a silt-stopper pre-filter, I clean these every 9-12 liters of water. Without a silt stopper, every 2-3 liters. Its a good idea to attach the cleaning brush to the bag or filter. They tend to get lost otherwise, although MSR will send you replacements free as well. Mine get hard use by teens however with some upfront training so they know when to stop filtering and clean them, these have provided a lot of water for the group very reliably. I've since added a Mini-Works EX because of the ability to screw directly to a Nalgene. Nice feature and no spills!
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