Give him some time but if he does not improve then yes, I'd give him back. Sometimes a chicken or rooster does better in a different setting, different group, sometimes they don't acclimate. Just like people, they have their own personalities, too.
I have 1 Polish hen with a mixed flock. She is a skittish spazola, even though no one ever bothers her & the large RIR & Comet Rooster, Casanova, protects her as if she was his baby chick. She often runs under him & he looks bewildered & worried while gently preening & chortling to her as she is underneath of him. The other hens are like...what's up with her?
I've watched them, it's as if she's running from an invisible ghost. Her hairdoo has been trimmed so she can see better, but she still runs like a spaz. She knows she is smaller than everyone else, so she naturally takes precautions to avoid possibly getting picked on, but no one has ever picked on her. I believe it is just her spazzy personality trait.
Perhaps your Roo, because he is a Roo, feels like a vulnerable spaz so he is acting out the opposite, to nip anyone else bugging him, in the bud. Or he may just have a mean streak. I've had 15 Roosters of different breeds, (currently 10 Roos of various ages, as my old original boys have passed on), & they all displayed the "tough guy act" at some point, but in time, usually about 2-3 yrs of age, they eventually became very comfortable with the entire flock (including Guineas) & calmed down.
As to my only Polish gal, the only time she is breifly fearless is when I have some treats in hand, squash, mealworms, etc., but 90% of the time she is zooming around as if her tail was on fire. She has a bestie, a smaller than average Barred Rock hen, who always has a bewildered expression as to why her friend is zooming around...alway looks surprised when Phyllis jets off, looking around, like...who the heck is she running from? It is hilarious actually....chicken TV entertainment. Oh, Her name is Phyllis Diller, of course.
Give him a bit of time to adjust, once he realizes, hey, "we are all birds here...not a threat. Save your aggressive behavior for foxes or falcons." He may calm down & realize his flock is family. But I would talk to the gal you got him from, keep her in the loop, in case he needs to relocate to a different family.