It is illegal to use in most sanctioning bodies.
For very small bull ring tracks it has a great advantage. This is why the quarter midget world uses them (track size and under HP'ed.)
Last time I personally used one on a kart was back in the '80's on indoor coke syrup tracks.
Keep in mind that you lose the braking effect on one side of the axle and you are now down to one tire stopping the car -- (looks real awkward when you spin.)
Thanks,
Brian Carlson