I am using it these days and I've found it wanting compared to Ecto. The only thing I think is great about EF Core is automated migrations, but in practice that's not where the complexity lies. It's in all the odd queries you need to make to satisfy the business logic as it evolves.

Edit: Probably the other good thing about EF Core is the designer, which as you mentioned is great for Rapid Application Development. Not really a time saver vs coding as the application scales, or if you prefer reasoning in code vs visually. Would like to see Ecto feature more user friendly tooling like a designer and automated migrations in the future though.