Dirt Devil Plus Model 523, which was the first Dirt Devil hand vacuum with a two-speed motor; it was also marketed as the Dirt Devil Pro Series Model 533 (in blue) for authorized Royal dealerships. (Sold in the years 1986-1991.)
Also: the Dirt Devil Deluxe Model 501D, essentially the all-metal Royal Prince hand vacuum with Dirt Devil branding. It was said this special model was made from leftover 501 parts that were destined for the scrap heap. (Sold in the years 1991-1993.)
~Ben