MongoDb vs Elastic Search for text based search in a collection

We are trying to weighing the benefits of using Elasticsearch for text based search on MongoDb
Vs
reading data in mongodb using text based indexes available in mongodb( app also have Redis cache)

Our Collection in the Mongodb includes documents that have data stored in html format
However the search is not within the html content.
We have other fields that include a topic name in each of the documents .
Topic name is searched to get the correct html content based on user entered text
We also have plans to use redis cache and the application would read redis cache for performance perspective

Any suggestions ?