It may look impractical, but if he uses the duster in this way, he will have both hands free for other tasks.
By the way, this drawing is very similar to "Rear End Roomba", a drawing I did for Devin Dickie. You can find it on Twitter (or Nitter, if you don't have a Twitter account). I also recommend you take a look at Devin Dickie's Patreon.