I welded on an Ultra-Fab 2" roller to my 4" drop receiver hitch which I need to flat tow my vehicles. It does indeed drag on some driveways, and the roller helps in those situations.
When I don't have the drop receiver installed I cannot recall my unit ever dragging. If it did I would likely add Ultra-Fab's bolt on rollers to the crossbar of my hitch.
Here is a link to my roller on Amazon:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1