Thanks for links. I had no idea. I tried flying an RC copter some time ago (piston engine) and getting it to hover was a nerve-wracking triumph. These folks and electric motors have taken it into another dimension.
The exhaust plume of a nitro doing the same things is kind of more interesting IMHO, it's like a telltale in a wind tunnel test. I'm surprised they don't put a smoke bomb on the electrics during these demos.