I once bought 500 g of CBD isolate for only 200 bucks and did a couple little sketchy small scale experiments with zinc chloride at equal ratios at a few different temperatures and I either cooked it and got a gross black liquid with a bunch of unknown crap in it and exo thc or I only got a percent of two of THC. I never really dialed it in. I could have sold a ton of legal edibles lol but like then thca came around and I was like eh whatever. So I still have like 450 g of cbd lol. Sometimes I call myself the cbd fairy and throw the powder around.
If the reaction is done right, tested, separated via distillation or chromatography and tested for impurities there's nothing wrong with it. THC is THC and I don't think HHC or D8 would have any more ill effects than d9 thc so long as they are clean extracts. But the aspect of conversion from a non-legal standpoint is just stupid. Why grow CBD flower just to convert to THC when you can just grow THC flower? This is only a thing due to prohibition and the 2018 hemp bill.
I personally think there's nothing wrong with HHC again so long as the reaction is done right and separated properly and tested. I've tested HHC disty and it's sometimes actually legit legal unlike D8 disty. And it also seems cleaner. But I haven't tested much.
It really is a problem that small companies can make really bad extracts with lead and other hazardous stuff in it and sell it in edibles. If a gummy ever tastes strange (other than weedy) from a hemp company I wouldn't eat it. It isn't a requirement to get safety testing on those and it's shocking how much lead hits show up in these small companies products who actually do choose to safety test it.
Basically there's no regulation. I find personally buying from well known larger companies they have good chemists who know what they are doing in terms of extraction and you can find good stuff (look for coas and cross ur fingers lol)... but this stuff being sold in gas stations etc from unknown small companies is really sketchy.
HHC, D8, D9 and D10 are so chemically similar I would be shocked if (clean) products containing them were any worse for you than natural D9 made products. When you start messing with putting acetate groups towards that 5 carbon chain (THC-O) or messing with lengthening the 5 carbon chain thcp, h, jd now you are really changing the molecule enough that long term effects are largely unknown. Push it any further than THC-P... like THC-P-O now you're basically just reigniting the whole K2 thing and that gets sketchy.