The annular wing is an interesting touch. It should reduce induced drag at the low Reynolds numbers these drones typically fly at, by eliminating the wingtip vortices. I was working on a very similar design for a while, and I placed the props at the wingtips to cancel the vortices instead.

Also it would be interesting to see what their power electronics look like. You get a 20x reduction in thrust demands by going from hover to flight mode, but the problem is that the efficiency of brushless motors also tends to be absolutely dreadful when you run them at 5% throttle.