The feather control was added to the spot brush in LR5.2RC and is a most welcome addition. However, I am still unable to achieve a smooth transition using the spot tool. Here is an example, with the setting as Heal, Feather 100%, Opacity 100%.
As you can see, the boundary transition is still visible.
I did a little testing, and can see how the feather works. It does not appear to be capable of a sufficiently gentle transition.
Does anyone have any tips on how to eliminate the transition boundary?