If you're just trying to get it hovering indoors a few feet off the ground, there's really a pretty narrow RPM band you need to be concerned with. Why introduce the added drivetrain loss (however small) and weight of extra gears?
According to the teams website, they think the extra hand pedaling increases the amount of power the human pilot can put out around 10-20%. Sounds worth it.
As to the recumbent position, I'm just guessing but maybe it has to do with stresses on the frame (which looks like it's barely up to the task of supporting the pilot). On upright bikes riders often have a tendency to mash the peddles, rather than smoothly spinning them, creating highly directional and varying forces. A recumbent position limits the amount of force you can apply to a single peddle.