In my research, one of the features I came across that I really liked and wanted to incorporate into my design was the folding arms. Since I had to build my quadcopter in sections no larger than about 6 inches, this was an easy decision.
The 'shoulder and arm' design worked well for me. I did redo the shoulders so that the arc of travel was increased to a little over 90 degrees. I also rounded the edges of the arm.
Changes I would/will make to the arms would be an internal wire channel and to thin them out a bit to reduce interference with prop wash. I would/will also change the design of the shoulder to give it a more retro-futurism look.