Astropad is a wonderful piece of software. It's well-designed, performant, and does exactly what I need it to do and does it well. That's especially great because I can't even find any other apps that actually let me use my iPad and Pencil as a drawing tablet (except for Apple's built-in Sidecar), so I'd still pretty much have to use it even if it weren't as good as it is.
I don't consider Sidecar a real alternative because it doesn't work on Windows, which is where I have to run all my 3D software since Apple's break-up with NVIDIA. But I still use Astropad on the Mac since, so far, I usually get lower latency and better responsiveness with it than with Sidecar.
