Hi Andre, yes that is the expected outcome for that function, and that is correct that it is not intended to be used for STL conversion.

It's not a general purpose importer that can work on any kind of polygon structure, it is meant to be used on a polygon mesh that has been constructed as a control cage for subdivision surface modeling.

A sub-d control cage should be a lighter weight polygon structure that primarily uses quads, not a set of dense triangle polygons like you have in your model.

There's an overview of sub-d modeling here:
https://www.youtube.com/watch?v=ckOTl2GcS-E&t=4s

This function is meant to process the kind of quad-dominant polygon structures that you can see in the video. It is able to convert those control cages into smooth NURBS surfaces so you can use them as parts of a model that you are constructing in MoI.

It's basically a bridge between sub-d modeling and CAD. But it is specifically for sub-d models, not triangle mesh models. That's why it is positioned in the UI in a SubD tab and not in the general File > Open.

- Michael