I've had lots of instances in the past where metal shutters would become damaged, possibly from a bad drive mechanism or physical stress. When metal shutters deform, they won't return to their original shape, creating the risk that it may detach inside of the drive. Plastic shutters, in my opinion, are much more resilient to this kind of stress as the material is more inclined to return to its original shape.

I understand opinions that plastic does not feel as premium as metal. But when it comes to the protection of a disk, I've always felt that plastic shutters were much better.