If you do a search you will find a plethora of info on this. As I'm here: I looked into the various options: Chigee, Capuride and INNOVV. Chigee seem to the the TOTR and best quality from what I could gather, but they are also the most expensive at around £400 or more. Capuride is the by far cheapest and I've heard that they look and feel it, too, compared to the Chigee.
Personally I went for the INNOVV N2 (6.5") and am pleased with it. It sits perfectly above the TFT without obstructing the view of it. It's heavy, solid made out of CNC aluminium, and the screen is..... just OK, but then again, it sits above to a far superior quality TFT. There is a version (N3?) which has cameras. I will admit that I have had mine on there for about 30 kms so far, but I'm about to embark on my first tour of the year and I'm sure I will find out if it has any deep flaws.
I think they all do the same and they all have a BMW cradle version (be sure to make sure you order that version) which allows you to use the wonderwheel. Compared to the BMW offerings, I noticed that the wonderwheel is just ever so slightly clunky and imprecise, but not to an annoying extent.