Simple answer is that Toad for SQL Server was built from the beginning to cater to DBAs and Developers who need to manage their SQL Server-specific platform.
That is, if you need to compare and synchronize databases or objects, debug your stored procedural logic, reverse-engineer DDL scripts from the database, alter any objects, etc. then Toad for SQL Server is your product.
Toad Datapoint was built for Analyst-types who need to work with data, and is not platform-specific. So the product focus is all about data, not about managing your relational environment.
With Toad Datapoint, you can access a wide variety of data sources simultaneously (even non-relational sources!), easily build queries (even across different data sources!), compare/sync data, visualize the data, conduct profiling analysis on the data, and much more.
Hope this helps you make the right decision.