This tool comes with a Drum (a rubber cylinder) and 4 replacement bands (the disposable sanding/grit surface that goes on the outside of the drum). The bands will be need replaced with regular use , and the drum should only need replaced if lost or damaged.
The only difference I could see was the accessories. The N/8 comes with shop-oriented accessories and the PT forces you to purchases the accessories you need for your type and size dog. Since we purchased the tool for a small dog, I bought a pack of the smallest sanding bands which worked out great!