Here are PGroonga users.
Zulip is a powerful open source group chat. It uses PGroonga to implement all languages support full text search. Because PostgreSQL built-in full text search feature supports only one language at the same time. PGroonga can support all languages at the same time.
waja is an EC for fashion items. It uses PGroonga to implement full text search by keywords.
Here are main reasons to use PGroonga:
It's easy to integrate with existing search process. (waja uses PostgreSQL.)
waja only needs to add indexes to use fast full text search.
It's fast enough.
PGroonga also supports query expansion and auto complete. Their precision can be improved by maintaining normal PostgreSQL tables. It's easy to use.
See also the blog post by the developer. (Japanese)
(Send us your service description, how do you use PGroonga and why did you choose PGroonga.)
You can send your use case from https://github.com/pgroonga/pgroonga.github.io/edit/master/users/index.md .