There is actually a lot of overlap in the feature set. When I moved from MSSQL to a gig that was all Postgres it was fairly smooth to do so, the main differences being OS related. Thus you don't need to switch over entirely to add a useful tool to the toolbox.

MSSQL has some advantages in parallel query execution and data warehousing enhancements - if you can afford the licensing for the latter. The other view on that is you can tip up as many Postgres production instances as you have hardware for without impacting the software budget.