Cute idea but certainly very limited application. For one, who has a contiguous garden made up of almost flat wood-chip base nicely bordered and easy for the Tertill to navigate? I don't. In order to make the Tertill work in your garden you will have to design your planting beds to be friendly to this robot's operating methodology..... Almost flat surface of fine wood chip base, perimeter edges/fence that the Tertill can recognize and know when to turn around, and then keep an eye on things because weeds do have a habit of also growing right next to other tall plants.
I'd rather they made an automatic lawn-mower and not just concentrate on weeds (unless they already have such a robot). And throw in a weed-killer reservoir on the back and have it spray over suspected weeds as it passes over them. Let it maintain the lawn autonomously, cutting the grass a little each day for the entire season. That would seem to be more practical and have a wide range of use across most lawns.
I like the concept, but it seems you have to really design your garden from the beginning to be Tertill-friendly or it won't really work.