Hi
What context where you thinking of applying it to? Are you looking at a new feathred friend for yourself?
I have success with two IRN's, a cockatiel and a lovebird. It took training, time, and careful management - still does!
It depends completely on the individudal parrots and their life stories, the setup you have, and yourself and your experience, mannerisms etc.
Personally - we won't be having any other parrots for a very, very long time (
Remind me I said that next time I feel sorry for one listed, won't you team!) I know we are lucky to have the dynamic we do. If we did add to the flock, it certainly wouldn't be bigger than an IRN.