Sawyer inline purifier filter

I've used it.

Good:

Effective against all 3 types of baddies — viruses, bacteria and protozoa.
Fairly compact
Easy to suck (as an inline filter)
Gravity feed option

Bad:

No carbon element — so foul tasting water will still come out tasting the same (may not be an issue if you hike in places with decent water sources)

Ugly:

Needs to be primed (flushed with faucet water using a faucet adapter) prior to use. Not just the first time, but anytime the purifier element has dried out (i.e. whenever stored in-between trips). If you don't flush prior to use, then it's extremely difficult to get water through. This is what happened to the reviewer you linked — he flushed his purifier when he first got it, but didn't flush it again prior to his trip. Carrying a damp purifier means more weight and more mess — but you will have to with this purifier.