A great advantage of STV is that it needs no parties. That means it can be used by organizations which haven't any, such as unions, clubs, and schools. And STV voters are never constrained to parties. They may ignore party labels and mix nominees together, ranking a Blue party candidate 1st, an Orange 2nd, another Blue 3rd, and an independent 4th. Most people want PR when they understand its benefits.
Voting is easy.
Sorting and counting ballots for STV was hard, but free software now makes an STV tally easy for any group.