mycilial mass for co2?

ive seen a few things around about them was wondering if anyone had tried them. they claim it produces 1500ppm for 6 months.
i struggle to accept that unless we are talking about a completely sealed environment with absolute dead air.
and i wonder how safe introducing fungus into your grow areas. my experience is that fungi and my plants dont play nice together.
Any thoughts would be appreciated.

no one? or is it just one of "those" subjects? i did a search i didnt find anything on it.