Aquatabs are not chemically the same thing. From their web site: "They are effervescent (self-dissolving) tablets, the US EPA approved active ingredient is NaDCC which is also known as Sodium Dichloroisocyanurate or Troclosene Sodium."
While Portable Aqua has Potable Aqua Chlorine Dioxide Water Purification Tablets and its active ingredients is clorine dioxide tablets.
See http://en.wikipedia.org/wiki/Chlorine_dioxide -- lots of references, etc. on this.
See http://en.wikipedia.org/wiki/Sodium_dichloroisocyanurate -- this is so new, hardly any information exists.
I did find these two references at cdc.gov:
Lantagne DS, Cardinali F, Blount BC. Disinfection by-product formation and mitigation strategies in point-of-use chlorination with sodium dichloroisocyanurate in Tanzania. Am J Trop Med Hyg. 2010;Jul 83(1):135-43. Link: http://www.ncbi.nlm.nih.gov/pubmed/20595492
Jain S, Sahanoon OK, Blanton E, Schmitz A, Wannemuehler KA, Hoekstra RM, Quick RE. Sodium dichloroisocyanurate tablets for routine treatment of household drinking water in periurban Ghana: a randomized controlled trial. Am J Trop Med Hyg. 2010;Jan 82(1):16-22. Link: http://www.ncbi.nlm.nih.gov/pubmed/20064989
This newer product works in 30 minutes versus the worst case wait for the chlorine dioxide tablets of 4 hours (but only 20 minutes if you pre-filter with a 1 micron absolute filter for Giardia and Cypto. I like the .5 micron nominal filter for $4 that weighs 1 oz from DudaDiesel.com (use a wire clipper to remove the steel ring at top to get weight down to 1 oz).
I'd like to hear from more educated, chemically and biochemically, medically, about this newer chemical form.
I believe though this newer chemical is the cause for the one product no longer being distributed. REI has switched to this newer chemical: