A a potential customer both for personal use, and as a spaniel club(s) member who occasionally is tricked into being a test committee member or chair, I can tell you that we would
very very much prefer that you have flight pens for your birds if we are buying them from you. Even just for training use for my own dogs, I want to be semi-accurate in assuming that they will fly. If I need a non-flyer for a particular training method, I'd rather clip the flight feathers myself rather than find out - surprise! No steadiness training today! sucker bird!

We have a smallish flight pen just for the damn dirty pigeons we keep around for training. They are much better for training when they have access to flying, even a little.
I would also SUPER BIGTIME prefer to occasionally keep Chukar around for training rather than the damn disgusting pigeons.... Chukar can be disgusting too,* but at least I can eat those.
*{Yes I know you can eat "squab", but no I won't.}