https://youtu.be/MNnB_50Z20I?t=553s
Previous HN discussion: https://news.ycombinator.com/item?id=33949895
Similar design MIT patented: https://news.mit.edu/2022/lincoln-laboratory-inventions-win-...
To be fair, the limiting factor might be manufacturing capabilities, given most attempts were using 3d printed propellers which results in terrible surface finish, compared to injection molding.
Mountains/ sea: expensive deliveries, lack of infrastructure, long delivery time, easy environment to navigate, less competition.
Urban: cheap deliveries with plenty of existing infrastructure and competitors, complex and dangerous environment to navigate.