I tried the Aquamira Frontier Pro a year and a half ago and tossed it in disgust after one trip. Even with clear mountain stream water and frequent prefilter changes, it kept plugging up until it took 20-30 minutes to filter a liter! I also found it impossible to suck water directly through the filter (one of the suggested uses)--my jaws ached excruciatingly long before I got enough water even to "wet my whistle." There are times when you don't want to wait half to three quarters of an hour (15 minutes for the chemicals and another 20-30 for the filter) for a drink!
I also did some research on this filter. If I'd done the research before buying the filter, I never would have bought it! There was no information at all on either the packaging or on the Aquamira website as to filter size (how many microns). IMHO, this lack of extremely important information is absolutely inexcusable. I finally found the info after considerable searching of the McNett (parent company) website--3.0 microns.
Now go to this reference: Center for Disease Control: Water Disinfection for Travelers
. Go down to Table 2-29, which shows the filter size needed to filter out various microorganisms. Note that while 3.0 microns is sufficient to filter out giardia cysts, it won't filter out cryptosporidium cysts, which have come to be as much of a threat as giardia. Crypto, like giardia, requires several hours of chemical treatment to kill.
In other words, I paid for and carried around a filter that wasn't doing its job, even in conjunction with chemicals.
There are other filters that can be put into a gravity system that will do a far better job than the Aquamira Frontier Pro and that don't require chemicals in addition to the filter unless you're worried about viruses. My current gravity filter (homemade) consists of a Katadyn Hiker Pro filter cartridge, with the excess plastic housing trimmed off, inside a Sea-to-Summit Ultra-Sil dry bag, using 5/8" connectors and tubing from US Plastics and a couple of flat rubber washers from Lowe's. It is very similar to, but quite a bit easier to use than the late lamented ULA Amigo Pro filter. It weighs 6.5 oz. dry, considerably lighter than most pump filters, and filters a liter in a little over a minute. I plan to try it out with a Sawyer filter, which would save another ounce of weight.