Not sure which version you are referring to.
If you have the original electronics from Inventables (Arduino/gShield), both the J Tech version (0.9g) and my version will run on that set up.
The difference is that with the original Inventables grbl and the J Tech 0.9g grbl you have to load the version that does what you want to do, either spindle (Inventables) or J Tech (gray scale laser). Then you have to re-load to do the other function.
With my version of grbl you only load the firmware in once. Then to switch between laser and spindle you change a few $ parameters. No re-load.