I can't remember when or where I read this, but I remember reading a study that concluded that the controlled napping in the flight deck being far better than forcing oneself to stay awake and end up microsleeping on finals (which has happened to the participants who were tired but denied sleep in cruise) in terms of safety and crew quality of life.
I really feel that controlled napping is far safer than forcing oneself to stay awake, subsequently not feeling clear in the head or risking microsleeping at critical phases of flight.