It exists as a sequel to 1997's Revolutionary Girl Utena to celebrate its 20th anniversary, and thus takes place 20 years later. Because of its nature as a 20th anniversary celebration, it was never going to be, well, revolutionary, but that doesn't mean it isn't enjoyable or doesn't have some interesting ideas.
These three chapters are essentially about the spirit of Utena helping the student council members heal from their lingering trauma left over by the events of the main story. It doesn't line up with the anime's plot details 100%, but it's Utena; no two versions will have the same details.
A common criticism of this manga is that it is hard to believe the characters haven't changed in twenty years, but to that I say: trauma will do that to you. Utena is a series about trauma and how it plants its roots in you and fundamentally changes you as a person, and this manga shows that (although I do agree that the character designs not changing after twenty years is a bit silly. As I said, it's not perfect).
Ultimately it doesn't have the time to deliver everything I could want out of a follow up to Utena but considering its only three chapters, it uses its short runtime wisely, covering just about everything that needs to be covered, even if it cannot get to everything.
It is a poignant and heartwarming story about how the effects of trauma are long lasting but it is never too late to heal. It's not perfect, but for what it is, it works well.
