What's wrong with it is, when I extend with a new subtype, I have to fix up the locations that use the type. Potentially all of the locations that use it - I at least have to look at all of them.

With the polymorphic approach, I just have to create the new subtype, and all the users can do the right thing (if they were written with polymorphism in mind, anyway - if they use virtual functions on the base class).