The feature list for Huagati DBML/EDMX Tools reads like a defect report for the related Microsoft products. There is no bloat here, everything is a must have for many shops.
LINQ to SQL Features
First up is a no-brainer, updating LINQ to SQL diagrams when the underlying database changes. One would think Microsoft would provide this out of the box, but since they didn't this alone makes this product worth its price.
Huagati's tool is also more intelligent about honoring default constraints such NewID and GetDate. Exclusion rules to prevent unwanted tables and columns from being repeatedly suggested round out this feature.
Since developers might not want to apply the changes right away, the tool can generate a report showing the differences, a comparison report is also available.
Naming Standards
A major problem for both LINQ to SQL and ADO.NET Entity Framework is that it does not handle naming standards. Using Huagati's tool, developers can specify rules such as when to strip off prefixes, how to case property names, and whether to remove underscores.
Documentation
The final feature is again something Visual Studio should have had but does not. The tool can automatically create or update an application's XML documentation using the table and column descriptions from the database.