My bet is that one of these things couldn't be approved by the EPA in the United States, ever.
Not relevant. The carbon in our feces came originally from the environment and will eventually return to it whether it is burned or decays.
No net increase in carbon.
As opposed to fossil fuels, which add carbon that had been locked up below ground for megayears. Net increase of carbon in the ecosystem.
We can argue about the effects of adding carbon by burning fossil fuels, but not about whether it happens.