My Spike has a Flight suit (don't kill me ><).
We use it for taming purposes and around people who don't want to get pooped on. They're very useful as my conure has his wings clipped and hence cannot fly to his perch. Also he is like a human, he watches t.v, eats, talks to us, walks around the house and always wants to meet the people that come over.
He prefers to sit on the couch to watch t.v or groom us and in this case, a diaper is of great use to having a little people bird going around. He never quite got the hang of the poop command so in this case it's win win. He doesn't mind it either as I don't have to go running back and forward with him and no more cleaning my couch.
That's just my oppinion and it is really helpful in my household.