Add nodes extension: unit indicator wrong

The 'Add nodes' extension says it uses 'px' as the unit for the node distances.
This is correct in a px-based document, but incorrect in a mm-based document.
It seems to use the document units.

If that is true (and also works when the object is grouped and transformed), one way would be to use 'document units' instead of px in the label.

The better option would be to allow the user to select a unit.