Most importantly, do the Arduino/microcontrollers posses "real-time features" due to their simplified electronics? I am surprized, shocked even, at how well the Arduino/GRBL seems to be overcoming this biggest hurdle...real-time pulse consistency.
Microcontrollers are 100% real-time and deterministic.
You should be shocked at Windows/Linux CNC controllers. :~
You can also see TinyG
which I have been told (by no less an authority then the author of TinyG) is much better then GRBL.
It looks like they also have a version for the Due.