Roosters are not necessary to get eggs.
Roosters like ANY other Chicken, you can get good ones and you can get bad ones.
They can be VERY mean, yet not all are.
They can be VERY protective of the girls, yet not all are. I have seen some outrun the girls heading for the coop or safety when a predator comes around, so NO they are NOT automatically great keepers of the flock. Again, it depends on your bird.
I have seen a rooster, his name is Sam, who will try to hop up on you, people who do not know Sam, think he's being aggressive, NO he wants to sit on your lap and you pet him, and give him snacks. He's a bigger roo, so that probably scares people too. Having 10 pounds of flapping feathers coming at you !
I have also seen Sam have a FIT and actually try to fly after hawks sitting in trees !! He will fight them and I firmly believe to the death, though the 2 hawks I seen him get it on with, ran pretty quickly.
There was another rooster, who's name, I will not repeat here. Was an A hole and would attack, would sneak attack too. That one got whapped upside the head with a frying pan and made into lunch.
They crow, almost constantly. You may not mind, if you have neighbors or an HOA, THAT will be a huge issue.
They have sex, constantly. If they pick a favorite bird, it can hurt her after a while, tear her up. They can be rough when they have sex. Then can be quite the gentlemen too... it depends on your bird.
Different species have different traits and tendencies, but again at the end of the day EACH bird is unique.
If you do get one, good luck and I hope you get a good one, because when you DO get a good one, they are very lovable pets, IF you can put up with the constant crowing.
Aaron