Slighly better than original Rated 4 out of 5 stars
I think this alternate and the original both find the same duplicates when same options are used, I tested it on TB6. The trick is that this alternate version has even more options to search duplicates and some little things that make the life easier, mainly: resizeable window, clearer interface & recycle/delete option. Although it is marked as incompatible, it works perfect on TB6.This review is for a previous version of the add-on (0.3.7).
It's more than slight!
Well, they're not so little, these things... for example, being able to sort by different comparison criteria affords you control over which message you would like to keep out of each set.
Anyway, the biggest difference, albeit not one visible to the user, is the fact that removedupes (alternate) is _Free_Software_. That means you have the legal right to improve upon it if I, say, get a job and don't have time to work on it.