The "through-loading system" (implying a two-part central rear backrest segment featuring the cup holders) is one of the cheapest options!
It's just mainly intended/advertised for those who wish to transport two passengers seated comfortably in the rear with long objects put between them. If you intend at most one rear passenger along with long objects, the basic two-segment rear seat backrest is just sufficient. I also read the three-segment rear seat backrest further compromised vehicle rigidity, affecting handling, FWIW.
Passengers in a properly driven BMW should need sinks rather than drinks!
