Do you know what this reminds me of? The movie _Spun_, only this isn't a dark comedy, it's a documentary, it's real.
I'd say this is a difficult watch, but not a hard watch. It has explicit drug use, so don't expect someone to say "I'm going to shoot some heroin," then there's a cut, and we cut back to them high. No, you're going to see everything.
What may be most strange is that for a documentary as raw as this, I thought it would feel more intimate, but maybe it was the frantic editing that made it seem more detached. In addition to the drug use, there is a lot of nudity, and sex - possibly even rape.
Somehow I don't think the average person is going to stumble upon this; I think people who are familiar with Valentine's work will seek it out.
If you're bothered at all about the subject matter, stay far away. Otherwise, this is worth a watch or two. I honestly hesitated a while before hitting play on _Black Metal Veins_, but I'd say it's more sad than "shocking" or "disturbing." Just the idea that these are people, addiction is real, pain will pass down through generations, no one asked to be dealt the life they have.