I’ve been a user of Astropad. It really was an exceptional piece of software which greatly increased the useful value of owning an iPad with the Apple Pencil. I also own a Wacom tablet, but I could much more easily use Astropad for quick work. It wasn’t perfect, the primary shortfall is you get latency with the drawing. With Sidecar that doesn’t happen.

Astropad deserves credit for shipping a feature years ahead of Apple adding it. That in itself is worth a lot. At the same time, the functionality is very obvious. The real lesson here should be something about expecting to be copied from day 1. Anyone that’s been around for a while knows that is just reality. You don’t get special credit for having an idea first or producing a working product long before someone else. There are patents and trademarks but those only go so far. The more obvious what you are doing, the more likely other people are working on it even if you don’t know it. History is littered with that sort of thing.