From the website quoted above (Technology research and development_Beijing Linyi Yunchuan Energy Technology Co., Ltd), an excerpt translated by Google:
Aerodynamic layout of the lift body duct
The wind energy capture efficiency that exceeds the Betz limit increases from about 50% to more than 60% under strong size constraints
This represents 20% more than the wind turbine without a duct. I measured an even greater difference with a torus of 42 cm outer diameter and 24 cm inner diameter, the inner part of which is funnel-shaped.