I'm using a cassette toilet for the first time this year. Happy Camper made an enormous difference in the smell when I empty it. Very little smell now.
I assume that when it says organic it means in the chemical sense, carbon-based, rather than in the no pesticides sense. (And yes,the definition of organic for foods is very tightly regulated.)
Formaldehyde is a carcinogen.
I find it hard to believe that anyone is going to breathe enough sewer gas to get hydrogen sulfide poisoning.