the misdirection might be the most brilliant piece of writing ive ever seen. Audiences are told prior that its about the mansons so you enter the film with built in drama but NONE of the tension is generated by the film itself; its all created by the veiwer so when the film subverts that expection and reveals that "once upon a time" was literal its a wild revelation. Never seen anyone work an audience like that.
I would hate to have the factoid spoiled prior because my concern is without the premise established externally the film has no stakes and potentially no plot.