This is actually pretty cool, with some solid engineering - general idea is to tap the wind when you can, use an embedded quadcopter to steer and lift when you can't. They claim tumbleweed has a porosity gradient from top to bottom which allows it to pick up more wind movement than if it were even porosity everywhere, so the little guys are engineered with a similar bias to help get the most out of wind. I imagine it's .. not great .. if you're headed into the wind.