Scimitar shaped propellers haev been around for a long time - early 1900's. The shape gives certain advantages (sound profile, greater chord thickness, a higher maximum power/disc load ratio and they can take a higher tip speed) and some disadvantages (reduced maximum efficiency and a sharper efficiency curve).
See
Scimitar Propeller, Symitar Scymitar simitar prop, AmericanParagliding.com - Powered Paragliding for paragliding use.
See this older thread
http://www.pprune.org/tech-log/39965...-aircraft.html