A recommendation for the rear mount rack
nice pics showing that the factory install is definitely the preferred route to go. (I had posted the original pictures of the dealer-installed option on my 135 vert).
One recommendation for you and anyone else with the rear-mount rack, please keep the vertical bar in the upright and locked position when NOT carrying a bike. If the bar is folded down, in the unlocked position, the quick-release levers are likely to unscrew themselves due to road vibrations and fall out. I had one fall out and it was nearly 3 weeks to get a replacement since BMW doesn't actually make the rack and the small parts like screws are not part numbered items.
Hope you enjoy the rack.