Confirming previous reviewer, the module is a lot slower (~ 20-40x) than other alternatives like Array::Utils or List::MoreUtils when you want to perform basic set operations like union/intersect/diff/symmetric diff.
One of my go-to packages on the CPAN. It's a fantastic tool for building and comparing sets of arbitrary values. If you find yourself trying to shoehorn hashes into your ideal data structure using keys() and map(), you might consider using this rich, functional OO interface instead.
A very nice module, with a sound functionality and documentation. Although one can do easy set operations with some hash and homemade code (see Cookbook), this module provides the comfort one
wants sometimes when needing functionality fast.
The CAVEAT characterizes this module best: "The first priority of Set::Scalar is to be a convenient interface to sets. While not designed to be slow or big, neither has it been designed to be fast or compact."