I wouldn't risk a trunk mounted rack option on your M5 IMHO. OBTW I have one and you can have it if you wish. It's not any special brand but we used it on some of our other cars in the past.

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"What you hear in a great jazz band is the sound of democracy. “The jazz band works best when participation is shaped by intelligent communication.”
Harmony happens whenever different parts get to form a whole by means of congruity, concord, symetry, consistency, conformity, correspondence, agreement, accord, unity, consonance…….