. . . when the duct opening is at the floor level in between the baseboards? These are all possibilities that should be explored . . .
If your air return is on the wall right at floor level and you want a metal unit, then these are a great way to go. We fold over the top and edges to form kind of a shoebox lid effect. We can make the projection whatever you want, but typically it is either 3/4 inch or one inch. There are 18 different patterns to choose from and 6 finishes. They are provided with color matched screws. These are also available for locations that are not in between baseboards. See those here.