On my own router I have three e-stop buttons around the machine, wired in series. They supply power to a relay with multiple contacts which switch the "enable" signal to the stepper drivers, switch power to the relay which supplies power to the stepper driver supply, and send a signal to the estop input on the motion controller. I should also switch an enable signal to the VFD but I ran out of control wires to the VFD... This is a big advantage of using the estop button(s) to switch a relay - a relay with multiple contacts can then switch multiple different items. Essentially using the estop as a mains switch is a bit brutal - but easy, which is why it's done. However, you are now relying on the reliability of a single component, the relay, to guarantee safe operation. That is why a safety relay is recommended - these are designed to be as reliable as you can practicably achieve and are used for things like safety gate operation. They are not cheap (although I was lucky enough to pick up one as obsolete and damaged packaging which is why I use one). If I were doing it again, I would use a pair of standard relays arranged with coils in parallel and contacts in series or parallel (depending on what they are switching) to give a poor-man's safety relay equivalent. The commercial safety relays include quite a lot of internal complication that is not really required for a machine like this (such as supporting duplicated estop wiring).