

My guess is that the wires/tracks could get stuck in sewage, and it might make it harder to examine the floor better due to how small the drone might be.
I had the idea of a monorail system, but I guess it would have a similar issue in case the surface the rail was attached to got faulty. Might’ve been cool looking though.
I can also recommend Pimsleur. A bit more expensive, but features more traditional style courses, while offering a lot of what Duolingo has. Plus actual topics with grammar, not just random words!