Hello GOwin – awesome comparison of those tools. I am one of the developers at HeiGIT of the Sketch Map Tool, and we are always glad to receive feedback.

One small correction I would like to make (or maybe I misunderstood you): We do store the original sketch map and the uploaded sketch map with markings on them on our servers. The first one, we need to be able to do georeferencing of the sketch map after it was uploaded. The second one we store to be able to improve our machine learning models which are responsible for detecting the markings. We do point this out to the users (see text on the upload dialog). But it is not possible, even with the right URL, to download any of those files one day after they were created. So data is stored on our server, but the risk of accidental disclosure of private information is also minimized.

I also want to share that we are aware that it is tedious to create multiple linked up sketch maps for a large area (similar to the atlas feature of Field Papers). It is something we would like to address in the future.

Again, I really enjoined reading your post. ~ Matthias