Beard hair yield in the scar should be about 60%. When we add Acell and PRP into the scar, we have seen the yield increase to over 60%. Beard hair is quite coarse. It usually blends well in the donor area and mixes well with the other hair, but it is different. It tends to be quite wavy too. This means that if you grow it long, it will become even more wavy. When you have straight, fine hair, this can be an issue. When the hair is cropped tighter, the beard hair is more natural in appeance.
Some people love the curly nature and the coarse hair. I think it usually looks ok in the scar. I think on the top, it looks better when the hair is kept short, but then again some people like it curly and long.
Nape of the neck hair can work. It is not optimal because it may not be permanent. It also tends to be an area where people often cut their hair short so extraction sites might be more visible. when you have no other option, the nape is a good source.
Beard hair has worked well in the scars so far. it's not for everyone, but i've not had a patient complain yet about beard hair in the scar. that does not mean that it will not happen some day.
Hair off the neck really does not seem to grow well. Use scalp hair first, beard hair second, and all other sources as a trial and third.