Svenestron:
That design of blade is on the Bell 430, MD900, EC-135 to name just three. It is very nice - low vibrations and low maintenance.
The Bell 412 rotor head design story will be buried somewhere in a paper given to the American Helicopter Society. It was the start of production multi-bladed design by Bell, and the 406 and 407 built on that experience.
Like everything else, very complicated in the design, but very simple looking in the end.
And in the intervening years, a lot more was learned about composite materials and their strengths and weaknesses.