Personally, I’ve never taken to Machete order. Being deeply familiar with the films myself, I don’t derive any benefit from breaking the flow of the OT by jamming the PT in the middle for the sake of avoiding spoilers. If I were to have a marathon by myself or with friends who have already seen everything, I’d go chronological, likely skipping the PT or using fan edits. If I were introducing someone to the saga, say, to cram for VIII this December, I’d show them the OT and TFA in rapid succession, followed by R1 if they’re into it. If whoever I’m showing the films to in this scenario is interested in the prequels, I’d show those on their own day after the fact. I’d never force them on anyone, but I do think they’re worth a watch for new fans simply for perspective. It would be a mistake to muddy someone’s initial viewing with them, though.
Even knowing the Vader reveal, the prevention of that spoiler isn’t what I like about Machete Order. My favorite things is that you see the Luke’s story play out quite a bit in ANH and ESB, you get hammered with the crazy reveal. Then you see Luke’s father rise and fall to the dark side. And then both their stories come to head in ROTJ. It adds a lot more emotion when I view it in such order.