CEO of Vantage here: You're correct - and we only charge for EC2 savings realized.
Additionally we give away all other service recommendations for free: RDS, Elasticache, Redshift, etc. These are your savings and you should realize as much of them as possible.
We also have a suite of visibility and reporting tools for AWS, Azure, Datadog, Snowflake, MongoDB, Databricks, etc. Most customers prefer using Vantage as a one-stop-shop FinOps vendor and in general we find significantly more in savings at a fraction of the cost of other vendors.