How easy is it to introduce ducks to a chicken flock?

Asking more experienced chicken/duck owners, have you ever brought chickens into the flock? How easy is it for them to get along, and how do I know the chickens are being friendly?

Our rooster is very nice if that helps, he’s friendly to me and my dog even though we recently got him from someone else, so not mean to new things.

They got loud for a bit then seem to have lost interest-