Hi Serif guys, what a great and powerful iPad app you've create, absolutely love it!
I hope the picture could make my thoughts clear.
When you do retouching work on iPad, Clone Tool/Healing Brush is a must tool, and you need to constantly change sampling points around the target area to avoid repeating patterns.
Use the finger hold and wait few seconds, choosing sampling point, then raise your finger and put the Apple Pencil down back to the screen to retouch the target area is LOW-efficient and Inaccurate.
Also, while using brush tool to paint local color, we need constantly sample certain color near the Pencil tip on canvas, that means Eyedropper-Brush Tool quick switching in a flash.
In desktop environments, like Photoshop, the function key Option (Mac) / ALT (Windows) on the keyboard does the job perfectly -- press the function key, use wacom's pen tip to sample in tiny area on screen. We have Apple Pencil and iPad Pro now, but we don't have that Cintiq (or Intuos) experience yet. I just couldn't find an efficient method on iPad version Affinity Photo to switch between relative tools.
So, can you consider adding a shortcut key on the screen? Make it a functional on-the-go retouching and painting tablet.