They are meant to fit in the back of a light switch so are very tight on space. I opened one up, it's not very complicated but the routing is probably a bitch.

I actually know how to make PCBs and 3d print cases and stuff. I have 2 printer (I barely use them though). That being said, it is using main and if it fucks up and something catches fire, I think insurance companies wouldn't pay out. I don't think its worth it, but I did legit look into it and have like 2 half prototypes in kicad lol.

But ya, I don't know. I don't really want to touch stuff that doesn't just run on a small battery or off USB. Simple mistakes can snowball fast with higher voltages.