IF you try a roo, I suggest an older fella too. That way his personality is already set, and you'll already know that he's good with humans and has courtesy for his ladies. I have little patience for the rude, overly hormonal antics of cockerels, and neither do my hens.
Sadly, there's no safe way to know for sure whether your hens will mesh with a new roo or not until you try it. And then of course if it didn't work, you'd have the responsibility of dealing with him. I will say, it does change flock dynamic. If you're used to being the center of their world, you will see a shift of that somewhat. If you enjoy the sound of crowing, it's nice.
I tried a roo when my girls were around 7 mos. of age. He was 9 mos. Several of them hated him. He was young, hormonal, and bigger than any of them, so it got pretty ugly at times. My BO's comb would end up bloodied from resisting, and my EE took to staying inside the coop because she was afraid of him. It was very stressful and ruined the joy I'd taken in my flock - so he was rehomed.
I tried again the following summer - this time a two year old bantam fellow. After his quarantine period was over, it took all of 5 minutes of chest butting and they'd all accepted him. He was polite, and didn't attempt mating unless a girl squatted for him. He's not much for predator protection, but my girls were always good about that themselves.
If you try a roo, and can't get an older fellow, I'd suggest a bantam. At least if he's hormonal, he can't bully them too much...