I have a MSR Microfilter that I use while backpacking, which works well for me. It does require some effort, but I like that it screws onto my nalgene bottles to reduce spills.
I was debating between it or a Steri-pen, I went with the MSR because I didn't want to have to rely on batteries for water.
I also carry iodine tablets as a back up, just in case, but they need time to work.
Boiling, likewise, requires time, as well as additional weight for a stove, or additional effort to gather fuel for a fire.
I keep a lifesaver Jerry can around too, although it clearly is too bulky for backpacking trips. The stated life of the filter on these cans is 20,000 liters, which is over 5,000 gallons. I think that is quite adequate to meet my shtf needs. lifesaver-jerrycan