It does look like the complete plug and play solution.
I just can’t help but think I could make less bells and whistles version. Maybe a arduino micro $4, some ir optical sensors $7/10, and a zero point ssr $??30?. This kind of stuff is not my strong point and I could never sell them because I don’t want to get anyone zapped, but once its all wired up the programming is simple. I almost bought some parts yesterday to try it. There is a part on tindie that is close to the zero point ssr, but not close enough. I’m not positive it is the right way to do it though.
Having a speed controller is cool, but the PID is what brings this way over the top, it would really make any “spindle” a much better cutter. Although if you get one of the actual spindles with a VFD adding PID would be simple with an optical IR rpm sensor.