BackdoorArts
Senior Member
This one is a little quirky. It's a brush tool within the gradient tool, so depending on what you're doing it doesn't mask as much as it allows you to apply a set of opposite effects to what the gradient tool does. I only started messing with it today, but it's a brush tool and not a pure masking tool, which I would have found more useful. That said, there's a strong possibility I'm using it incorrectly.
Yep, user error. With the brush you need to click on the Erase tab and set that appropriately. I think you can probably do some wild stuff with it if you experiment as it will essentially serve the same as a Brush tool but within the confines of either the Radial or Gradient filters, which could be set up to "mask" the brush tool as well. Probably more confusing than trying to do the same thing in Photoshop (which you have with the CC), but it's a nice little addition.