How long are you keeping them? It might be a lot easier to use food coloring to mark them. That's what some hatcheries do if they mark chicks before they ship them. They put a drop of food coloring on the forehead.
I don't know what color down or how many groups you are looking at but you have many options for marking them. Even just using one color a drop on the forehead, the right side, the left side, the small of the back, the forehead and right side, etc. gives you a lot of groups. If you keep them long enough for them to feather out you will have to remark them, keep an eye on that, but you don't have to worry about a band getting too tight as they grow so quickly. I'd think marking them would be quicker than banding them. It would be for me.