There is a DataGrid component in the free Flex SDK. The AdvancedDataGrid is part of the data visualization package that comes with Flex Builder Professional. In general, the Flex community thinks the AdvancedDataGrid is garbage. Slow, messy, and written by engineers that aren't part of the main Flex team who don't follow the official best practices. There are functions in its classes that are hundreds of lines long. I'm not kidding. I know guys who have written their own implementation of the features in AdvancedDataGrid because it sucked so bad. Thankfully, most use-cases for a DataGrid will be handled just fine by the regular DataGrid in Flex.
The clash of ideas is the sound of freedom.