My first thoughts are to ask what has been your history with predators? How many chickens have you lost and, if you know, to which predators? Do you free range or are they penned? Is this really a problem? If you did keep a rooster what would change in the way you would manage them?
You can never tell if a cockerel or rooster will turn human aggressive. They can be fine until they are not. People have been keeping free ranging roosters with their flocks for thousands of years. If a lot of them were going human aggressive on a regular basis chicken could be extinct but they are not. But some do go human aggressive. If you are willing to eat him, sell him, or give him away if it goes bad you probably haven't lost much by trying. But if you can't get rid of him when it is time but just let it drag on you are at more risk.
In my opinion a rooster doesn't add much to the safety of the flock. Some might attack a predator, maybe a hawk, but that's not going to do any good against a fox, dog, coyote, bobcat, or most other predators. They certainly do not stand up to hawks every time even when they are present. Some of my hens sometimes scatter out so they are not all with the rooster all the time anyway and he cannot protect them if he is not around. Same thing is true with a livestock guard dog. If a LGD is not with the flock it is not doing much good.
When a threat is detected my roosters tend to try to lead the flock to safety instead of fighting a rear guard action. I've had two different dog attacks lost 8 and then 5 more chickens. In neither case did the rooster lose a feather.
Some roosters tend to be a lookout, especially against flying predators. He can warn them if he spots a danger. But many times in a flock without a mature rooster the dominant hen does a lot of looking and alerting.
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One thing I notice. If something concerns them the rooster will often get between whatever they are worried about and the flock. He kind of checks it out which does put him in danger. A humorous example, I can walk around with a bucket in my hand without a problem but if I am holding a small camera that they are not familiar with they go into this alert formation where he is between them and my camera. But if the threat turns out to be real he is putting himself in danger.
To me any additional safety a rooster brings to the flock is pretty marginal, especially if you have a dominant hen doing most of these things anyway, but there can be times having a good rooster can help.