Your guess is pretty much it: Postgres full text search is great for simpler scenarios, but elasticsearch provides more powerful search capabilities and simpler

Your guess is pretty much it: Postgres full text search is great for simpler scenarios, but elasticsearch provides more powerful search capabilities and simpler implementation of complex features (such as "search all shops in this geographical area with products that match these words the user typed".) That said, I've had good results with both systems, and always found the elasticsearch query syntax pretty arcane and difficult to put together from the docs. The docs essentially assume you are very familiar with Lucene concepts and that you'll be able to figure out what goes where in the JSON object from your past experience. If you are implementing a simple tag system, then I'd use Postgres first and only when performance becomes an issue move to elasticsearch.