I agree with you, in the sense that I'm not surprised if the pure-Perl List::MoreUtils::uniq doesn't blow a naïve implementation out of the water, speed-wise; but, like dragonchild, I thought that at least by using these functions one should get handling for unusual arrays, such as those containing arrays references—and this code doesn't provide that (or, at least, doesn't do so any better than Justin's original implementation).

UPDATE: A conversation with dragonchild showed that my meaning was a little unclear, so let me try again. I realise that the existing code does correctly return objects, rather than their stringified versions, but it seems to me that it could incorrectly confuse (say) the string "ARRAY(0x18045c0)" with an arrayref.