I don't own an ipad but I often use an android tablet as a touch screen for my pc (with spacedesk application). As my PC isn't on my keyboard, I place the tablet on the music stand and the pianoteq control is very interesting.
However, pianoteq's touch control is not perfect.
Changing instruments by sliding the image horizontally is excellent, but switching from one preset to next or previous is problematic, the arrows are too small and the proximity between "previous preset" and the "mark as favorite" star makes selection very random. Vertical dragging of the picture to change preset would be a great improvement (in which case you'd have to change the method of accessing the "engineering section" panel, I think it is possible).
Another thing I regret is the absence of an icon in a corner of the interface to instantly toggle to full-screen mode (as exists in almost all software).
I hope this message will lead to an evolution of this already excellent interface.
PS : Switching from square to landscape format of the basic interface would also be welcome, I'm so sad to see all that screen space lost...

Thank you
Yves
Translated with DeepL.com (free version)