This device though doesn't have the density of a brick, and it is aerodynamic: failure modes wouldn't be an uncontrolled freefall, it would be a stable glide.

This device though doesn't have the density of a brick, and it is aerodynamic: failure modes wouldn't be an uncontrolled freefall, it would be a stable glide. You could fail-safe this by adding parachute pyrotechnics which require an active command signal to not deploy: that way the worst case total electrical failure of a drone would immediately deploy chutes to slow it down. This seems like a much more acceptable control then the failure mode of a car: which weighs 2 tons and contrary to popular belief only stays on roads by convention.