Just did this to my Porsche. Very cool to be able to preview the look before making it permanent with paint/powder coat. Plastidip looks pretty good, but definitely not quality like you'd get from powder coating. Pretty amazing spray on stuff though and a fun project. The glossifier helps a lot in completing the look. The M5 wheels are pretty complex and have some tight spaces, so I would definitely recommend taking the wheels off the car to do it.
(I would post a pic, but our "new" Bimmerpost mobile client still doesn't support photo upload
)