(Ben, I tried to PM you on this but couldn't get through. Check your profile and try PMing me again).
OK, so I got my Frontier Pro the other day and did a little preliminary testing and wasn't too impressed. Tonight, I had the chance to put the thing through several tests.
Test #1: Screw the Frontier Pro onto my Platypus 3L hydration bladder as "dirty" bag and hang.
Time to filter 1L = 7 minutes, 26 seconds
Test #2: I was rather disappointed with the first test, so I thought I'd remove the prefilter and see if I can improve the flow rate. (I also removed the tube on the clean end, I think).
Time to filter 1L = 13 minutes, 50 seconds
Test #3: Ah...Pressure = force x area. This time, I tried attaching 32" of Platy tubing ABOVE THE FRONTIER PRO via the screw-on adapter that is used to attach your hydration hose (Platypus sells, or did sell, this tube and adapter link as a kit to link your pump filter to your Platy hydration bladder). I had to hang the "dirty" bag pretty high this time to allow for the length of tubing.
Time to filter 1L = 2 minutes, 36 seconds
Test #4: Remove all the kinks in the hose above the filter so it hangs straight down.
Time to filter 1L = 1 minute, 56 seconds(!)
Test #5: Filter two liters at a time.
Time to filter 2L = 3 minutes, 30 seconds(!)
Conclusion: My initial tests confirmed my skepticism about the flow rate of the Frontier Pro. However, further testing has shown that the key to making gravity filters work is having a length of tubing ABOVE THE FILTER. I hypothesize that the flow rate is directly proportional to the length of the tubing. A 10' long tube would undoubtedly improve the flow rate even further. (Imagine your "dirty" bag being nothing but a long tube). I think the system could further be improved by using a better "dirty" bag. My 3L Platypus hydration reservoir is angled out the corner, so the flow rate is probably not optimized. The bags that come with the new Platypus CleanStream gravity system seem more suited for this purpose (they have handles for hanging).
Although, I can't figure out how their system would work if the "clean" bag is set up the way it is pictured on their website. (Shouldn't the "clean" bag be upside down?)
I do have some remaining concerns with the Frontier Pro:
1. Is the pore size really small enough to remove all protozoa?
2. How does the filter fare in freezing temps? (My Sweetwater filter is desigend to be stored in the freezer).
3. Can the filter be cleaned by backflushing it like the Platypus CleanStream? How will I know if the filter is still good?
4. Will the filter remove all traces of chlorine dioxide taste (treating the "dirty" bag is essential to make this system effective against microorganisms)?
5. Will the chlorine dioxide really kill off all viruses and bacteria in 15 minutes as claimed, since these will pass completely through the filter?
I still have to yet to make my decision, but it looks as if this system might replace my MSR Sweetwater (11.5 oz) for my Colorado trip next month.
Weight of Frontier Pro (after use, includes prefilter and "clean" tube provided in package) = 2.54 oz
Weight of Platy tube and adapter to link Frontier Pro to "dirty" bag = 1.41 oz
Total system weight (doesn't include "dirty" bag) = 3.95 oz
Lighter weight tubing in lieu of the (rather heavy) stock Platy tubing, along with a drinking straw of identical diameter to the "clean" side plastic tube included with the Frontier Pro would help to reduce system weight.
Sorry the photos came out so big.