I read a great interview with David Hockney where he said that every day he uses an ipad to do verious digital artworks which he just emails to friends of his for free since they cost him nothing and he does them for practise. In his case he had a custom app written for him but he doesn't use a custom input method.
I think it’s his main medium now. I went to an exhibition of his iPad works at the RA a few months ago. I was surprised how good they were and the different styles/techniques you can see him experimenting with.
Looks like you can get some really neat effects!
I remember using a similar 'frustrated internal reflectance' setup with perspex + IR LEDs + an IR webcam + a projector to make a large cheap multi-touch surface. You're limited by the frame rate of a camera+whatever processing needs to happen, which I imagine introduces a lot more lag than, say, an apple pencil. But it's a good cheap way to get a novel input device.
There seem to be some artifacts, alternating stripes, created sometimes when the sampling speed isn't fast enough to keep up with very rapid movements. That results are still interesting, but that's a feature to be aware of
You can see some of the ipad paintings here https://www.theguardian.com/artanddesign/2021/may/10/david-h... although I can't find the original interview about the process.