I use a Pilz safety relay which is tripped by e-stop and by fault signals from stepper drivers (particularly if one of the dual X drive steppers stalls so the machine doesn't tear itself apart). The relay was a cheap "new but obsolete" one that cost £25 from eBay, which is the main reason I used one. However, it has multiple contact sets so I switch the stepper enable signal and the CSMIO motion controller e-stop signal (both of which should stop stepper movement almost instantaneously) and the stepper motor power supply mains input (which would stop steppers but not quite so immediately). One reason to switch the power is not so much for safety (although it was easy to do anyway) but to enable me to reset the stepper drivers in case one of them does go into fault condition. If a motor stalls (a rare event), I can reset by hitting e-stop and then resetting the machine. You need to consider how you would reset stepper drivers if they are configured to "fault" on error. Just a thought.