Very good call on the safety aspect of the Stop switch.
To have an E-stop fail when it is required to do it's job, is just un-thinkable.
At least if the wire feeding or coming from the E-stop break, the machine will stop.
Thing that worries me about the contact blocks that make up E-stop switches, is if they tend to be used as a means of turning the machine off as part of the operation of the machine, the actuator spring can weaken or in some cases break, therefore preventing the contacts from opening.
In a real emergency, I'd hate to be using that machine.