It absolutely does not “just work”, there’s so much to configure and then get-right for your use-case that you almost certainly need people with a solid understanding of the JVM + ES. Let alone fixing it when something inevitably breaks.
No more than any other database. I mean relative to SQL Server, Postgres, MongoDB or any other database. There's no extraordinary difficulty to manage ES above any other production system. It is very usable out of the box, and needs minimal tuning for many use cases. Of course some uses cases will require additional tuning and maintenance, sometimes quite a lot if you have a very large system, JUST LIKE ANY OTHER DATABASE SYSTEM.
In our case for a small website serving the general public (a few tens of thousands of requests per day) it just worked OOTB with hardly any tuning or maintenance at all.
We had a cluster. It was low maintenance. Any clustered / distributed database will require maintenance. At my current job we have SQL Server and there's a shitload of admin/maintenance required for that.