I can see their point with reducing the tip vortices, but not with a 90 degree bend. Thats not a very efficient angle to place it at. Also, props are designed to have the gratual taper from root to tip. This is the most efficient way for a prop to be designed (with today's information and technology). But an increase in tip speed, which would happen if you bent the prop 90 degrees, would generate a a bit more thrust, but I don't think that boost is worth all of the trouble and the saftey issues.