Not a big fan of the Kobutan. Don't know about where you are, but here in merry old England they are illegal.
But what I do carry is a metal bull-point pen (well, actually I try to have at least two in different carry-sites).
With a pen, the 'butt' end can still cause pain due to it's small surface area. Whereas the Kubutan is absolutly blunt at one end.
It's best use like a dullo-dullo. You can stab in all eight directions of attack, with a reverse-grip or sabre-grip... without changing the position of your hand on the weapon (pen!).
My favored grip is like this - I grip the shaft pretty much in the center of the pen. Seeing as I find the reverse-grip type stabbing motions most effective (for the close range) I have the point of the pen prodruding from the bottom of my fist, with the blunt end coming out as the 'sabre-grip' part.
When executing strikes from the reverse-grip, I put my thumb over the blunt end to stop the weapon sliding out of position or right out my hand. This dosn't mean you can't attack with a sabre-grip type motion though... all you have to do remove you thumb by sliding it off the blunt point mid-strike.
So you see... the perfect in-fighting weapon!
There is more you can do with it though, like joint manipulation in the event of the weapon arm being grabbed (it happens). Also a great gunting weapon if you practice enough. And there is also the screwdriver grip, carry sites, methods of deploying the weapon... etc etc. (I've spent a lot of time working on it) And the best part is, it's just a pen!
Peace,
Keeper