The PoKeys devices were not originally designed specifically for working with CNCs, but based on a very positive feedback from the CNC community, we started adding features to support such operation. These were all done in a form of firmware updates, which means that all customers that bought the cards, got new functions for free (we had to transition to newer 57 series hardware to give us more space for the growing firmware). PoKeys57E is now an ethernet-based general purpose I/O device and does not feature input/output protection circuits since it would limit other functions of the device. There are people (like danilom and others) that used PoKeys57E as brains and designed their own break-out-board for it to be 'prepared' for CNC world.
However, as you may have noticed, we (PoLabs) offer PoKeys57CNC device, which is designed for CNC. It offers some level of I/O protection (we are not using optocouplers on all IO) and its functionality is designed for CNCs.