I never kept any wild hemichromis.
So mike off for behavior a wild fish that has been growing for a couple of years, ie large enough to eat other fish will tend to eat the smaller fish if they can. Honestly I would say that the wild fish I do keep are more mellow towards other fish when I am around... BUT I think the key thing was when I am around. (Though I have a few that are just whimps.) Anyways I notice that my wild ones are the ones that hid more often when I am watching, or at least they aren't the ones in the middle of the tank trying to get fed when I am just sitting and watching. But I also noticed that they tend not to have nipped fins. Now does that mean they are very aggressive when I am not around? I mean I know that the real wimps all have nipped fins from the more aggressive ones going after them...
Anyways as for keeping wild caught. I honestly see only a few reasons too. 1) You just can't get them unless they are wild caught. 2.) You are breeding and want the extra bucks to say f1, or you just want to help keep the species true to its origin. 3.) You want to stroke your ego, ie being able to say I have wild caught fish...
I tend to only do mine for reason 1, since I really don't have the tanks to take breeding seriously. But that said I would never get say a wild caught christyi if I intended to put them in a tank with other smaller fish, I would just be afraid of them one night deciding to have a night snack. (Of course I still am afraid of my f1 christyi doing the same...)