In PD Pro 5.1b we added Symmetrical painting as well as Mirror mode. This has now been dramatically further developed and it's faster too.
Symmetry mode affects brushes when you paint.
Mirror mode also works with filters, not just your brush strokes. It also 'folds' an existing image into mirrored halves or quadrants. In other words, you can apply mirror to an existing image.
A new feature in the group of drawing modes is Kaleidoscope: choose 2, 3, 4 or more spokes, and start painting away. Internal brushes as well as custom brushes can be used in kaleidoscope mode.
Here are a few first impressions: