Although impressive, it adapts well to the 3DS XL, providing a very pleasant grip and even helps to keep the console in your hands. He's just a little heavy, a child will probably struggle to play comfortably, but for an adult no problem. The second joystick is very responsive.
It is unthinkable to play Monster Hunter 3 Ultimate without this circle pro (or other games like Resident Evil Revelations) as it adds a huge comfort and ergonomics appreciable gain.