This is a well thought out board with lots of nice features, like the optoisolators. It is very flexible and provides nice smooth motion. I had some problems zero'ing the gauge as it was not responding to the "!" command. The dev (boffin) responded to my questions which I find impressive seeing as I bought this almost 3 years ago.
I had to reflash the ATTiny to get the zero working and for me had to change the SwitecX25 library to get the zero working reliably. The motor would try to turn but seemingly not have enough power. It did move fine in normal positioning commands. This post https://github.com/clearwater/SwitecX25/issues/4 was the fix and suggested changing a delay constant used in the zero function.
#define RESET_STEP_MICROSEC 2000
I leave this here for any others with the same issue. May it save you many hours of googling about.