The thing that gets me (not in a good way) is the evidence that the amerindians used to just burn waste in a fairly random manner and bury the partially carbonised result to produce this incredible soil. They probably didn't worry about the few % of tars etc. involved as long as the plants survived and evidence from communal city gardens confirms that mild contamination can't affect fruit & seed at all, and only affects leafy stuff by rain-splash.
On the other hand we have the companies making money hand-over-fist from those newbie gardeners with more money than sense - how else could they sell "cleaner" charcoal ( I have my doubts) at many, many times the cost of barbecue charcoal?
A great idea with potentially massive cheap and cheerful benefits hijacked by bottom-feeding spin doctors preying on fashion victims.
Cheers.