I've encountered 2 issues when using ElasticSearch with Sitefinity 8.2.
Created an index of sitefinity products using elasticsearch -v2.1.1.
1. When ever you update a product in sitefinity, the index creates a duplicate of the same document, almost like a history of the previous state.
2. Sitefinity Search using the index created by ElasticSearch doesn't work. It can't find any of the values in the index.
It would be great if ElasticSearch can work the same way the Lucene search works. No duplicates and works with sitefinity search.