iPad Pro Duet Display & Aperture/Photos

Hi,
Just hoping that there may be some photographers/artists out there using the Duet Display app. I want to buy it and use it in the same way as a Wacom Cintiq, but just tentative, cause it's $30 on the Aussie App Store, so want to be sure.
I have an iPad Pro 9.7 & an Apple Pencil and was hoping that someone could clarify if I can use the pencil on the iPad for brush adjustments in Photos or Aperture or any other apps. I assume Duet Display is app agnostic(from the Mac side) ?
I figure this would be a lot easier than trying to use the mouse or track pad.

 

Thanks, I saw Astropad as well and note that it does this exactly, but it's $46 on the App Store and seems to get a few questionable reviews re. lag and battery consumption. Hence, my look at Duet Display.