I guess ultimately then, it's how much do you trust the relay (or more so, the relay contacts) that controls the spindle startup! (I'd figured there'd be a little more 'conditional' scenarios involved before a spindle could be allowed to start)

The problem with an isolating switch, is forgetting to switch it back to the 'enable' position & then walking off (or forgeting to isolate it in the first place!)....but far better that then having my hands turned to mincemeat by a spindle relay contact closing while my hands are still on the spindle!