Omg... that is not even funny...
The ONLY reason to use X11 is - because it is a user safety interface. There are standards and regulations about this and they are also part of robotic standard of any civilized country. That little gimmick is a nice low cost toy for hobbyists but - it has nothing safe about it - those are $1 automotive relays, they are not safety relays, even if they were they are not monitored by safety controller and have nothing to do in a safety circuit.
Please don't do this... and don't try to recommend something like this again
using this piece of crap as a safety device is same thing as putting wallpaper over a large hole on the elevator floor.
Do it right or ... get out of automation field - you can hurt or kill me.