If you're looking for something smaller my advice would be to stick with Micropur tablets or count on boiling as a last resort. Any very small water filter is, by its very nature, going to plug up too fast OR won't be as good a filter as you need.
Ken,
I carry the tabs, I use the chlorine dioxide type and a means of boiling as well. I guess when it comes down to water I like to be redundant. Supposedly the filter is good for 26 gallons???
Maybe I don't know.
Thanks for your input.
Blitz