Making kubotans illegal in any jurisdiction is nearly impossible. It's just a stick. You have to ban all pens and AA flashlights too.
The simplicity of the kubotan makes me confused as to why people would manufacture purpose-made ones in the first place. Other than being a "talisman" self-defense item or just being "tacti-cool", there is little benefit over a AA maglight or a County Comm Embassy Pen (which comes in aluminum, steel, copper and titanium)