Everyone has their own opinion on this. I do a lot of wide outcrossing, and a lot of tight inbreeding. Mostly what I do is Aunt-Nephew crosses or something similar.
But I do not think it will cause problems unless the problems are already there hiding. I once made a brother-sister mating, then took a pair from that mating and mated them, etc etc for several generations. It will not hurt anything unless there is already something bad there.
I don't want to sound mean, but asking a question like that is almost like asking what kind of chicken is the best to get. Everyone has their own opinion, based on something they read on the internet.... but will little to no actual experience.
The real answer is: It depends. On your goals, and the birds in question.