Interesting. I let it run on a folder where I know there are duplicates saved (different exposures of the same shot) and while it did actually find most of those, it also claimed that several photos of completely different subjects were duplicates as well...
It can definitely be useful for tracking down extra copies of pictures, but make sure you look at the results before you delete anything.
Edit: I just noticed that it was running on "Loose" detection settings. I put it on the "Basic" option and it didn't pick up any of the false matches this time. It also missed a bunch of the real matches this time, though. I suspect the sweet spot is somewhere between Loose and Basic.