The G203 works great! I bought four of them last week and am perfectly satisfied with them. I changed a single jumper on the PMDX-122 breakout board to use common ground instead of common 5V and then changed the signal polarity in Mach 3. That's all that was required. When I hooked up my G101 and then my G100, I didn't do anything.
I also have some G202 and a G320. All of them work perfectly. However, in the future, when I need stepper drivers, I'll select the G203.