Compared with most (if not all) water filters on the market, it has many advantages, including: removes viruses; self-cleaning (no back flushing or brushing); 10,000 liters lifetime use (about 5 times the average); no removable parts; no home maintenance; screws onto the top of a Nalgene bottle or MSR dromedary bag (no special cap); and the pre-filter intake works under water or on the surface (which ever is cleaner).
But the bad news is that, compared to MSR's next best filter, the HyperFlow, the Guardian is: twice as heavy (17 ounces vs. 8 ounces); twice as big (8 inches by 5 inches vs. 7 inches by 4 inches; and 3.5 times the price ($350 vs. $100.
Conclusion: if you are going car camping and need a filter to last for decades, or to another country or equipping an expedition with a large number of persons, then choose the Guardian. But viruses are rare in the USA. For backpacking in our country, stick with the HyperFlow or other brand's similar filter.
