Does anyone know if killing weeds mechanically using a rotary tool like a drill work? For example, the 'Weed Spinner': https://www.youtube.com/watch?v=Ld96e0mOrs4 How come they aren't so widely used and pesticides are still the preferred choice?
That sort of equipment isn't effective long term, usually, though it probably works on annual weeds. These bits of kit may break up the topgrowth,but usually leave in place a bit of root material that then regrows - dandelions, for instance, have a tap root that certainly goes down six inches, even up to nine inches. Worse, even if they do mechanically break up some root material, if it's a pernicious weed such as bindweed, all that does is spread bits of root elsewhere which will then grow, making the problem worse. Dandelions can be dug out by hand by digging down to get all the root, but anything mechanical doesn't really do the job.
There is a theory that if you keep chopping the top growth off when it appears, the root eventually gives up, but with pernicious weeds, it means regularly repeating the process probably for 2 to 3 years, likely more.