I'm not sure I follow:

Sets of strings are very common when trying to create a unique set of strings or optimizing "name in set_of_names" lookups.

Regarding your benchmark numbers: I have a hard time following how they work. A simply "word in set_of_one_word" certainly doesn't make a good benchmark for these sort of tests :-)

You should at least test with sets of various sizes and include the non-matching checks as well.