They were right about what I was able to estimate with the measurements on the calibration card.
Comparing their M851.cpp file with the default Marlin 2.X one, they gutted a fair bit of the code.
Theirs is 44lines (with the Marlin license header), and the stock on is 99 (with Marlin license header)
Mainly they pulled out the parts that would let you see and set the X&Y offset. Since the module comes with a probe, it’s not super crucial. However, if someone wanted to change the probe type they were using or location, they’d definitely need to change those.
Not sure how I feel about gutting functionality of some of the core commands. I could understand adding functionality, but I’d rather see core Marlin code be left as is where possible, and SM specific functionality be added on top of it via includes and such. That would make it far easier to bring new Marlin features forward.
Hopefully such a thing is part of the cleanup process before they make it readily available to everyone without having to reach out to them.