The program goes through all the product (nodes) and adds each to an RSS feed, duplicates mean you have duplicate products, unfortunately this early version of RSS feed does not associate a product to a hierarchic category (taxonomy).
I do not think there is a better Ubercart RSS feed module at the moment, nontheless this module is very dated.

The version 2 in development has a database maintenance to remove rogue nodes, images etc . I found that in order to have an RSS feed of high integrity the database needed sorting, as various ubercart modules are buggy and leave duplicate entries floating in the database etc...