I actually grabbed both formats when they released because I'm weird like that. The PDF felt like a weirdly perfect choice for this one. The text is centered, very stark on the page, and it uses a lot of that Courier-esque monospaced font that made the whole thing feel like I was reading a report or a recovered document. It sounds minor, but for a horror story about digging up a corpse, that clinical, typeset look added a layer of coldness the generic, reflowable epub just doesn't have. I tried the ebook on my Kindle and the prose was the same, obviously, but the whole thing felt sanitized, just another block of text in my library. The PDF preserved the author's intended formatting as an object, and with this specific story, that object-ness is part of the dread.
I know it's not convenient. You can't adjust the font size easily, and reading it on a phone is a pain. But for a one-sitting kind of nightmare like this, the PDF is the superior experience. It's less a 'book' you read and more an artifact you examine. The ebook is just the transcript.