On a high level, ETL/ELT is about sending data from your SaaS tools into your data warehouse (you are reading from different tools). Reverse ETL is about getting data from your warehouse into tools (writing into different tools). Building ELT is a fundamentally different technical challenge than building Reverse ETL. Aspects like types, rate limits, and destination state (knowing whether data already exists in a destination) are unique to Reverse ETL. Visibility becomes challenging too as some destinations have unique quirks, like API contracts where you write to them but you don’t know if the write was successful or completed until later. Writing to tools also requires references between objects (foreign keys onto existing data, like mapping Companies and Opportunities in Salesforce) that aren’t necessary in the ELT world.

From a product perspective, the UX is very different as well. Reverse ETL requires a lot more user input (ex: mapping which fields to update in a tool), whereas ELT typically mirrors data using a standard schema (without much user customization involved).

We are close partners with ELT tools like Fivetran, and you can see our partnership post here: https://fivetran.com/blog/fivetran-partners-with-hightouch-t...