Since my OP I’ve learned a couple of things I’d like to share.
One of my reasons for trying the simulator was because gSender’s UI changes depending on if it’s connected to grbl or grblHAL. An example pertaining to the Vortex is mentioned here. Unfortunately it doesn’t seem like a 4th axis can be used with the simulator yet.
The repository for the simulator can be found on GitHub and the developer says it’s a work in progress and a ‘proof of concept’. It might get better over time.
The other major difference is that, as far as I can tell, the SLB and SLB EXT boards are running a fork of grblHAL called SienciHAL. I’m basing that on the Firmware & Flashing resource page for the SLB showing a version number that matches one on the SienciHAL repo. Sienci states, in the SienciHAL README that it is purposefully not under active development. The plan is to eventually switch to grblHAL once all the progress that Sienci has made is incorporated into grblHAL.
I wanted to make sure that anyone that tries the simulator is aware of these differences. It’s not perfect but short of having an extra SLB laying around it’s the best testing solution I’ve found.
I should also mention that the simulator has, like many command line programs, a -h option that prints the help describing the options available when starting the program. Just a FYI because I know not everyone is used to command line programs.