I can easily tell that all you did to make this model was delete the rest of the footman, because it still contains unnecessary parts.
By removing the bone, animations, and pivot point, I was able to lower the file size by 0.27 KB. That isn't a lot, but it makes a difference when you import a hundred attachments with these unnecessary parts.
I also noticed that you did not make the material two-sided. That can look rather odd if the head doesn't fill up the entire helmet; the player would look into the helmet and see empty nothing, rather than the inside of the helmet.
These complaints apply to all of your helmets...
I rate this a 2/5. If you fix these things, I will give it a 3/5.