The C Extensions I build are designed to highlight the lines of the scroll, not to compete with it with lots of heavy shiny bling.
My preference is for a simple ebony or dark hardwood stick, with black hardware. I never cut into a scroll, and rarely if ever use screws to attach the extension, preferring to use string tension only to keep everything in place.
My current lever design incorporates separate adjusting nuts for height and for tension, which allows for simple fine adjustment by the user to cope with different string diameters and tensions. I use a special spring washer to provide smooth movement.
The simplest extension is a stick and one lever for the E. Other levers can be added as needed.