Nasa ParaWing (NPW) have been mentioned on several topics including the present topic, including kites based on Rogallo rescue parachutes for tether-aligned AWES.
NPW are also used as power kites, including kites up to 150 m² for Windsled.
Originally their lift to drag ratio is about 2.5 to 3, without the tether(s).
https://www.2e5.com/kite/nasa/reports/
Page 7:
The maximum lift-drag ratio of the single-keel wing shown is about 2.5 while that of the twin-keel wing is about 3.
See also the curves of lift and drag coefficients, and lift to drag ratios from the figure 16 on
NPW are cheap and have an advantage: they pull very hard (perhaps due to their inflated parachute-like shape), but in a narrow flight window (due also to their inflated parachute-like shape). I will explain why it is an advantage.
The flying window is a bit smaller, partly because the NPW’s need a certain angle of attack to stay inflated properly but also because they weigh so little that there is no momentum in the kite that helps to expand its flying window when in flight.
The smaller flight window is presented here as a disadvantage. But I think that for AWE use it is an advantage because the trajectory of a kite crossing the flying window greatly exceeds the useful swept area. Moreover in yo-yo mode it is preferable to make U-turns at the limit of the flight window, during short reel-in depower phases. So a narrower flight window induces a natural flight limit, perhaps allowing several unities to be closer each other. Therefore a NPW wastes less space, and we can increase the density in a kite farm.