You're going to look at the 4 I'm giving this and think I'm telling you not to read it, but that's not the case. If you've already read The Promised Neverland, there's no reason not to read the one-shots while you're at it. The art is fine. The extra story is not bad. But I am at a complete loss as to what purpose they are supposed to serve.
I straight-up liked the prequel about Ray, but I found that I didn't have enough to say about it to warrant a review. Ultimately, it is a nothing. It is an extra chapter that depicts facts that
we already knew in a more direct way. In another series, I wouldn't think twice about it or this second one about Sister Krone.
But, holy shit, you're telling me that The Promised Neverland got multiple extra chapters to fill in details—three as of this writing—and they're seriously NOT going to address the abrupt and unsatisfying ending of the series even a little bit?? Worse, to finally turn to the issue with this Krone one-shot, they're going to add details that complicate the parts of the story where there weren't any serious issues? In this, we find out that not only was Krone no different than the other children, she once tried to escape. It was the failure of her escape that lead her to become the sadistic person she was shown to be in the original manga.
I feel like this critically undermines her and, by extension, the Moms as characters. Why would escape attempts be so common among the Sisters if the Sisters were chosen by Moms specifically because they were pliant and amenable to learning about the Farm process? Why would they kill off Sisters regularly if they only choose a select few of the children to become sisters in the first place and their purpose at that point is to give birth to the next generation of children? If this is trying to address why there were so many sisters, but only a few farms in need of Moms, it sure did a piss-poor job of doing so. Krone was not old enough to give birth during the course of this interlude, so it's completely unreasonable to hang the threat of death over these girls. Their purpose, from the perspective of the Moms, had not been served.
In isolation, the actual physical story told is totally fine, and the art is still great. But why the fuck would you add complicated issues like this to the series after the fact when the ending of the series is such a complicated mess that could use some extra attention in a one-shot like this?
(Edit: To be fair: after writing this, I realized that she had not actually become a Sister yet because that is signified by receiving the dress. This pre-Sister period was also shown in the manga, although I don't think it was put in exactly this way before. It's still just a weird premise to me.)