I have a Halfords Hi-Mount rack and it fitted real sweet on my Alfa coupes.
The big advantage, other than the lights and number plates not being obscured, was that the top part of the rack can be angle back to the same angle as the rear window, putting the bar that the bikes rest on angled back rather than horizontal.
So if one of the straps holding the bikes broke the bikes wouldn't fall off as they were 'hooked' on to the rack.
It was probably more aerodynamic as well.
I saw a version of that where it had bike trays for the bikes, like a tow-bar rack would. That looked a bit better but I couldn't see a brand on it. It was at Peaslake Walking Bottom car park.
I have seen Bones racks but they don't look that impressive to me and they need a light and plate extension don't they, to not be illegal?