I have the camera in question. It's rather discreet between the number plate lights but it's visible. Gives you a fisheye rear-view when you engage reverse, with guidlines for steering which turn with the wheel. It also lets you see the front and rear graphic for the parking sensors at the same time.
It's of limited usefulness. The fisheye view is unnatural and doesn't give you the confidence a direct view in a mirror does. You don't get a clear sense of where the obstacle is; if you'll actually hit it or not. It is however useful as a "fourth mirror" just to double check what's behind you, for instance if something's sticking out of a wall (it's saved me from backing into a broom an idiot hung on a wall with the long handle sticking straight-out horizonatally- the sensors hadn't picked it up). It works fine at night with the LED number plate lights and backup lights giving plenty of illumination to the road surface. There's very little issue with water obscuring the lens, even during heavy rainfall.
I have an issue with the software; after engaging drive again, the rear-view doesn't switch-off. It stays on for the duration of your journey until you press one of the iDrive's function keys to switch to navigation for instance. Otherwise it overrides anything on the screen at the time; if you disable the parking sensors and the graphic for them disappears on the right of the screen, whatever mode is visible behind it will appear squashed, and simply scrolling with the iDrive wheel won't produce anything decipherable. Split-screen mode doesn't work properly either until you disable the camera manually.
Overall, whilst it's useful, it isn't worth what I payed for it.