I don't want to be a downer on this because it sounds like a cool system, but it might be worth checking whats in the receipt paper as a lot of it is pretty bad for you:
https://toxicfreefuture.org/press-room/new-study-finds-toxic...
Even though bisphenol-A is banned in EU, I believe bisphenol-B is still allowed. I suspect - though I don't know how to research whether it's true or false - that everyone just switched to bisphenol-B, which is said to be either similarly, or more toxic than BPA... :(
Even assuming that "BPA-free" paper I'd buy is really so, and not just BPA-covered one imported from China and said/labeled to be "BPA-free" by someone somewhere in the pipeline...
You need to go out of your way to buy phenol-free paper. It's a thing but unfortunately it's a niche rather than the default.
If the labeling can be trusted it isnt hard to find phenol-free receipt paper on amazon.
However, none of them say what their actual 'active ingredient' is and I am curious if these are necessarily known to be better. Most of them describe themselves as 'plastic coated'.
Yes, the main problem is the paper with bisphenol, which has been banned in Europe.