I didn't know there was a documentary, but I heard that someone (a family member?) was going to publish a book on the subject.
He was a vile man with a sick sense of humor but he could still be pleasant company. I talked to him briefly (after Kurt died but I knew nothing about this detail) the subjects we discussed were mundane ("hey go tell those girls over there your uncle Il Duce just hit the lottery"). He was a decent drinking "buddy". He also sang and made jokes about rape (a notable example was when he appeared on the Wally George show).
I heard that he was virtually homeless and when the band needed him for a gig they would drive around until they found him panhandling. He might have been up for taking the hit, I don't know him that well (saw his band twice, talked with him once).
He dead now, he got hit by a train (according to the film, he died during production, one week after they interviewed him).
The film is still interesting to watch to see Courtney Love give death threats to a reporter and then receive a free speech award from the ACLU.