I'd stick with the major name brands for a water filter- MSR, Katadyn, General Ecology. Keep in mind that there's a big difference between water filters and water purifiers. Filters get rid of protozoa and bacteria, purifiers do that plus virii. You still need to treat with iodine or boil with a filter.
I've used the General Ecology First Need extensively (a friend has that one) in some nasty black scummy waters with no ill effects. That being said I bought the MSR filter. The GE clogged several times and a replacement cartridge is heavy. There was no way to field backwash or maintain it. The MSR is easy to clean in the field if/ when it clogs. I treat with potable aqua+ then filter. That keeps my filter live critter free. I don't have any experience with the Katadyn but it has a good reputation.
Gravity filters tend to be much slower than they claim (take a look at some of the long distance rafting forums- they seem to be the ones using gravity filters the most. They tend to have larger groups and stationary campsites where time and weight aren't an issue.). We've pumped for groups of 4 to 5 without an issue.
I see lots of claims listed from universities, but no articles cited or links to lab reports. They don't say how they are killing the viruses. .5 micron will stop bacteria and protozoa (giardia, etc.) but viruses are much smaller.
Concerns: I don't see any pics of the innards. How much filtering area is there? How many gallons of muck will it filter before clogging?
Can you get replacement filters now? How about in 3 years? With an off brand this is a concern.