When I was younger I often carried a kubaton until on vacation in NY city I was bording a boat to see Ellis Island (My great grand parents came that way) and as the metal detctor beeped the gaurd said this was an ilegal weapon and that it was to be confiscated and destroyed
. So I remained a somewhat defenceless 10 year old (with only 3 years of MA expierence) for the remainder of the vacation.
I do not carry one, as Bigkahuna said a flashlite as well as a dogchew, screw driver, or a pen will serve the job just as well and woundn't be considered a "weapon" either
As far as effectiveness goes a kubaton is near indestructable and will crush in a skull if needed but it won't do anything if you can't even carry it (legally)(I also never saw how effective the keys to the eyes would be) . As opposed to a pen which has the ability to puncture soft tisue (neck,eyes, etc.) and can be carried legaly so it can also be used as a lethal weapon. Though if your local goverment allows it carry a gun or knife instead.