I think you're mistaken about a few things. > Less efficient cruising due to much more drag from all the ducts and engines. So, I read through some of Boeings

I think you're mistaken about a few things. > Less efficient cruising due to much more drag from all the ducts and engines. So, I read through some of Boeings research in this area years ago. The array of fans ends up acting like an insanely high bipass ratio turbofan. In the case of hybrid aircraft the combination is more efficient when cruising. The efficiency of a fan producing a given thrust or drag goes up with disk area, as it can spin slower and the local speed mismatch to the airstream is less. The array of fans acts like a giant disaggregated disk in this regard. > Much less likely to fly with engine failures as they can dramatically affect control (since they are essential parts of the control system). These are electric motors and batteries. Electric motors are extremely reliable, and in this case we have a high degree of redundancy. This thing is almost certainly more reliable than a single engine helicopter. > Yaw (rotational) control is highly dependent on working engines on both sides. The flaps can help with that, it's not solely reliant on differential thrust. There's plenty of precedent for yaw control of flying wings. > The glide ratio of the aircraft would be very poor with all the drag, even assuming the surfaces were still controllable (not hanging). You can't evaluate aerodynamics by eyeball, and that goes doubly for active devices like these wings. It's the net circulation pattern around the wing that matters, and you have no actual information about that, just assumptions. Likewise that there's some novel fault problem with a movable flap just because it has fans on it. You realize airliners have huge flaps that deal with much more substantial forces?