Postgres is orders of magnitude safer, sometimes a bit slower, but requires a bit more forethought when it comes to planning a schema to match your models. You typically appreciate this more in maintenance and later development more than you appreciate it up front.
The general risk with any for profit open source company is either them pulling all the good features into the paid version, or suddenly changing your license so that closed source projects have to either stay on the old versions or pay for a commercial license.
