For all who are thinking of flashing the adruino with Estlcam: going back to GRBL is very easy. I switched from GRBL to Estlcam and back to GRBL a couple of times.
To save GRBL to the arduino, please visit the GRBL wiki page on Github: https://github.com/grbl/grbl/wiki/Compiling-Grbl
Summary of the wiki: Just download and import the GRBL files into the arduino ide. Then run the sketch from the GRBL example.
So this is it.
I use Estlcam Controller even for STL and Easel generated G-Code. So no need any other Gcode / GRBL Tools.
My workflow know is: Inkscape or Fusion360 or Easel => Estlcam for CAM and / or to control my X-Carve.
If you have any questions, please do not hesitate to ask