How effective is the Atkins diet in the long run?

I'm trying to lose some weight and someone told me to go on the atkins diet. Personally I'm a little concerned about it. My younger brother playes football for his high school and whenever he needs to lose weight in a hurry he goes the atkins route. The problem is he never stays on it and his weight jumps right back up. I want to lose some weight but, I don't want to go up and down like that. Does anyone know if the atkins diet is safe or is my brother just unable to stay on the diet?