Do I understand correctly that this would be perfect for playtesters to make and annotate a transcript of a Twine game?
A transcript that the tester can then edit and send to the author as a text file?
It doesn’t show each passage in the story once, like a proofing format, it shows a player’s path through the game. So if you have someone test your game, you can see where they went, and what they had trouble with, that kind of thing. It’s a common thing when testing parser games: they can produce a log of the gameplay, and testers can insert notes of what they were thinking or problems they noticed.