The nozzles straighten the flow (which otherwise comes out at an extreme angle) to allow the diverter fins to more effectively aim the airflow at the target.  The scalloped nozzle outlet was necessary to eliminate an unpleasant hissing/whooshing noise in earlier prototypes.

INSTALLATION: Remove the vent diverters by grasping the outer bezel and twisting it a quarter turn or so counter-clockwise, at which point they should easily pull straight out.  The first removal will be more difficult, as a small dab of hot glue is applied on the interior during manufacturing.  Ensure you can remove your vents before ordering.  Install these by aligning the retaining clips with the gaps in the diverter assembly and clicking them into place.

Manufacturing variability will cause different vans to have slightly different airflow characteristics, but the recommended configuration is:

2nd row: Left - 2 nozzle, Right - 4 nozzle

3rd row: Left - 8 nozzle, Right - 6 nozzle

4th row: none installed

Printed in ABS. 

Solid models available free of charge (personal, non-commercial use, for people with a 3D printer) released under Creative Commons BY-NC-SA license.  Download here.  No warranty given or implied.