I think that for an emergency situation, bleach or commercial chloride-dioxide makes the most sense. Thousands of thru-hikers rely on bleach alone for all their water purification needs for months at a time. Although I haven't thru-hiked in years, I still keep up with the sport and things haven't changed in this regard. While the CDC is probably correct in pointing-out that bleach might not be 100% effective, there has been no clinical research or quantity of anecdotal reports that I'm aware of to make me concerned. A two-ounce dropper bottle will hold enough bleach to treat 300-600 liters of water (depending on whether you need to use two or four drops per liter, which itself depends on how clear and clean the water is to start out).

That said, I still prefer to filter. It is quick, easy and effective. If space was not a concern, I'd pack a good quality water purification filter with a field-maintainable cartridge over any other form of water purification. And I'd still bring the bleach or chlorine-dioxide tablets and a metal cup to boil as backups.

I used the Frontier straws. They seemed to be effective, as I never got sick, in spite of their poor efficiency ratings. The Frontier Pro works better than the cheaper Frontier, because you're not walking around trying to suck out of an open container, and also you can squirt water into a pot for cooking. But these are one-trip devices, and probably not a long trip either. You can also turn the Frontier Pro into a compact gravity-filter setup. Search YouTube if you're interested in that. I actually still have one of these gravity setups in my older vehicle emergency kit.

The SteriPen has interested me for a while. The appeal is it is a small, easy-to-use device, with short treatment cycles that will sterilize all biological hazards in water. My concern is the risk of relying on an electronic device that might fail when needed most, and it doesn't address water taste. But even a filter can fail, hence the need for a backup.