They are slightly different styles of blades. As I remember, the 721 Slimeline was a Walmart exclusive. The blade and handle on the 721 was more "rounded" and had a bit of a more streamlined feel. The 722 Spitfire was a more beefy blade in comparison with a more "blocked" off design. I am on shift atm but once I get home, I can provide a side by side of the two I have.