I have been tempted to try Eco One or The Natural, which Doc sells. It seems to work just fine if you use a little dichlor with it. Chas experimented with Eco One a while ago with daily reports on the Doc's forum, if I remember correctly. Chas sent Vermonter a water sample to be analyzed. Again, if I remember correctly, the water was fairly pathogen free, but not as much as a chorine tub. That is why I believe a little chlorine is necessary.
There are enzyme users that swear by the product. It is supposed to be easy on your skin, smell good and easy to use. Three reasons why I have shyed away from trying it are extended filter times, weekly rinsing of filters and high pH (it likes a pH of about 8 which just seems unnatural to me).