It seems to be 1/2 will report "no problems at all" while the other 1/2 will report various problems, from anything like guineas will constantly harass one chicken/just the roosters/just one color or be quite aggressive to almost everything. Many had to rehome the guineas due to ever persistent aggression. My own situation.. guineas were fine, then for some reason suddenly started targeting ALL roosters. All roosters had damaged or nonexistent tails from the guineas trying to grab them to beat them up.. ALL the time. Getting rid seemed to help.. but not completely. They were much worse to the peacocks, I had to clip the male guinea's wings as he literally tried to kill him, no matter what the peacock did, the guinea was right there trying to take the skin off his face.. the peacock was just about ready to drop from exhaustion and the guinea was like the energizer bunny, constantly biting and pulling the peacocks face. Sure seems when guineas go bad, they go ALL the way.
It also does not seem to matter how the guineas were gotten or raised, either raised with chicks or raised by hen etc there are vicious guineas out of all methods. The odd thing is, if one batch does not work out you can cull all of them and start with a new batch and MAYBE that batch will work out.. despite everything else being the same. Back to 1/2 works fine, 1/2 don't.