What kind of environment will the user be in? A defensive weapon is something you have to carry on your body all the time, or you'll get assaulted on the day you decide to leave it home.

Also, with something like that, training is paramount. If you can find a good instructor, plan on 3-5 years before becoming effective for non-lethal encounters -- *if* you can get that good. After that level, you still have to be in regular training to keep your skills. If you're planning to fight a guy with a gun... Well, don't bring a stick to a gun fight.

You'll probably want to look into the law in your area to find out whether you can carry a stick around.