There's been a lot of discussions about this book in the Golden Age discussion groups. The authors are all well known even if not all of them are mystery writers.
The task was not easy: Miss Marple is a sort prototype for any senior amateur sleuth and Agatha Christie is the most famous of the Queen of Mystery. You also have to consider that those were golden age mysteries and the puzzle and the psychology of the characters was fundamentals.
That said it worked. I didn't love all the stories but it was interesting read how different authors recreated this iconic character.
My favorite stories were by Lucy Foley, Elly Griffiths, Natalie Haynes, Val McDermid, and Ruth Ware as they wrote stories that worked as mysteries and were also able to reproduce the GAD atmosphere. Please note that almost all of the are mystery writer.
I think it's up to the future readers to decide what worked and what didn't.
Many thanks to the publisher and Netgalley for this ARC, all opinions are mine