Remember, the purpose of an "emergency stop" is to kill power directly at the source. (As opposed to being an input to a digital readout, requiring the computer to act on that action. That is unsafe.)
That is why emergency switches are so expensive. They usually connect directly to the power, or a power-breaker, which has to handle high voltages and amps directly, and keep the operator safe from disconnect shocks. (When you abruptly stop power, the amps continue to flow, like momentum, and try to jump connections. Thus, the elaborate internal setups for industrial emergency switches. This often includes dual-line breaks, and a physical separation arc-gap wall between contacts. Possibly also some quick-snap springs to pull contacts to a non-arc distance.)
For these tiny devices, we don't need super-industrial, OSHA required emergency stop buttons. We simply need something that will handle 240vac @ 30a for most uses. It should be 4x your consumption. Though, you may want to get dual-contacts, and break the live-wire of the motor drivers/power and the spindle/power separately. Though, if they are all plugged into one location, like a power-bar or a rail, killing the rail is fine. (But you can get feedback from the spindle, pumped into your sensitive electronics.)
You do not, and should not, have to kill the computer. Just the power to the moving devices.
I got my hand crushed in a 6-on-6 web printing-press, hurt like a b***h because the one place that I was located, didn't have an emergency stop button. Every other location had one, except that one. So the conveyor grabbed hold of my rag, and pulled my hand inside the conveyor-belt, slowly... My hand wrapped backwards, popping and crunching, around a metal roller that was as wide as a beer bottle... Luckily, it was just tendons and knuckles popping. No permanent damage. It stopped when the circuit-breaker popped. No-one could hear me screaming.
You don't want to accidentally lean over, and your hoodie-tie gets grabbed by the 10,000 RPM spindle... Or accidentally "think" that it is safe to clear some debris, and the spindle decides its next move is up, and into your finger... and not have a stop-button handy for you to reach.