Does AsyncFieldMixin serve a purpose any longer? It looks like the pratical upshot is it stores Address parameter required in the Field constructor whereas a bare Field just throws that parameter away after using it to compute the field value; IOW Field uses less memory than AsyncFieldMixin, but that is all.

Yep, that's basically the sole difference

OK - and that's with intention then and AsyncFieldMixin should not be removed (and the incorrect docs just changed) or it can be removed?

Yep, that's by intention. We used to have AsyncField vs PrimitiveField as completely separate inheritance trees, then realized it was unnecessary: deleted PrimitiveField and replaced AsyncField with the Nixon

OK - I'll update the docs to indicate this purely saves memory vs deleting the mixin and storing Address in Field.