Just found this forum (bought a Ritter knife), and noticed it doesn't seem like anyone has heard about this product. It contains a flocculant (drops particles out of suspension) and a disinfectant. I've talked to a few people that have used it in relief work in Haiti and they say it works amazingly well, even in putrid water, it comes out clear and clean.

Here's a couple of links, first to their site, and second to a couple of CDC pages about it.

http://www.purpurifierofwater.com/

www.cdc.gov/safewater/publications_pages/options-pur.pdf
http://www.cdc.gov/safewater/publications_pages/pubs_pur.htm

Seems to me it might make a better choice in survival kits than simple chlorine tablets.