It's a great character controller that is near flawless. If you have the asset try the character playground scene with the ultimate character controller. You'll notice that your controller gets stuck in the geometry and will hiccup on stairs with just basic walking without crouching/jumping/etc. I imagine there would be more problems if you were to do that.
I attached a picture of some of the geometry tests included in the kinematic character controller asset so you can get an idea.