Can you get him to keep the birds a while longer before killing them? I
have a friend (retired game warden) who raised birds for hackles for
several years. He retired completely due to health problems a while
ago, and sold his breeding stock to a major distributor a few years
ago. Based on discussions with him in the past, 10 months seems kind of
young, as the quality of the feathers improve, up to a point, with age,
but if these are just barnyard stock, it might not make much
difference.

I've never done chickens, but I've done waterfowl, game birds, deer,
and even a little caribou, and I (shudder) agree with Wolfgang. It is
an interesting experience, but not something I'd do often.