Summary

A simple way to get better air flow under your MG4 (2022-2024) and not the new 2025 model yet to be available in Australia as of Oct 2025.
The model is simple to install on the underside of the bumper for each mounting bolt as shown by the photo of the items mounted to my 2024 MG4.
I would recommend the find be printed in ABS or ASA. PETG maybe used but bear in mind that the fins are subject hot environments and PETG may not last.
DEFINITELY do not use PLA as it will warp for even a moderately warm days.
To install:

1. Undo the bumper mounting bolt.
2. Mount the diffuser Top item to the bumper so that the curved part form fits to the bumper.
3. Slide the Diffuser bottom into the slot so that both slide pins allow for the diffuser rear to be slid upwards all the way up to the bumper.
4. Screw into the rear facing hole a M2 x 14mm screw/bolt to prevent the fin from dislodging.

Update 3-Jan-2026:
The bottom stl file now has version 2 where there are winglets which direct the air flow up to reduce the low pressure turbulence around the top of the bumper. This change further improves efficiency by way of reducing the drag coefficient, albeit a small amount but none the less may give up to some 10-15 kms over the normal range.