I have not even built one myself.
My brother is a mechanical engineer that designs/commissions power plants, and he’s played around with one at home, running a small engine with it.
The main thing, safety-wise, that you have to remember is that the main product is carbon MONoxide (the dangerous one, as opposed to carbon DIoxide).
This thing should be outside, or at least WELL ventilated.
There are pictures from WWII where farmers were running their tractors with them when no other fuel was available.
It does sound like it’s worth looking into. I found some fema plans and others. My hubby could probably build one, he’s pretty handy.