There are no rooster sanctuary, so most people give them away without knowing there outcome. Whether they become dinner or live life with a new flock.
Don't put too much expectations, it will save your feelings from being hurt.
Also it's difficult to give away a rooster cause most people...
I only use nutrena naturewise, from feather fixer to meatbirds based on a wide range on what is needed at time. The consistent purchase is there layer crumble or pellets and the all flock pellets. Very good product. The plus is that it makes there poop less stinky vs feeding them Purina all...
He's friendly to his previous owner cause this person raised him, your a stranger to him of course he's going to attack you.
The way to remedy his behavior is letting him get use to your presence and his new home. This process takes time because not all rooster learn as quickly as others...
Generally focusing on breed type, it's practical not to have any mutts "currently or future" in the flock. Unless your able to setup pens or large dividers to keep them totally separate. Just something to consider.