I use these with the gravity filter in the Boundary Waters. I always paddle out 50 yards or so from shore to avoid shoreline gunk but only get about 15-20 gallons per filter. Basically it is one 6-7 day trip per filter. I would recommend to a friend that has already has the gravity filter or hiker pump. Otherwise I would recommend going with a brand that has a cleanable filter.
This review was written in the old system and had content requirements that are different than reviews written today.