An easy way to dust them is just give them a pan full of masonry sand and just sprinkle sevin dust in it and they will dust themselves.It's best not to handle your birds if all possible.Also suet promotes feather growth and they love it.
In N.H.,Tony.
I have heard of using suet. I would think being that it is very high in fat that it is an occasional thing, as during a molt or the winter months only.