It definitely takes some practice, its a totally different way of designing, the mouse is easy because everyone is used to it, it is stable and doesnt float in the air, I remember they used to have that partial design software that had a floating pen, kind of like an old belt-driven handpiece arm. You definitely want a pen with touch sensitivity, this is crucial if youre designing crowns, the harder you push, the more you sculpt, but the buttons on the pen to change functions is tricky, which is why having a mouse connected also is important. The biggest problem Ive had is turning the model, you have to 'grab' by holding the button on the pen while you move, it can be tricky because the pen is actually the size of a sharpie. You will also need a very large desk if you plan on using one, or a keyboard style tray that slides out under the desk.