Please note a couple of things - this is not by far the first plastic lawn mower, but it is newsworthy because it was 3D printed. You will be familiar with injection molding products in our everyday life, we see them all over - the problem that injection molding has is that the plastic cant be very thick because it wont come out of the mold easily- and it is mass produced.
We don't have those cost or time constraints. And 6mm ABS plastic is very strong. The Cheetah is great for functional prototyping of real world products.