Hi,
I do not have any experience with the PoKeys 57CNC, but has a long history of good service with many users.
All development of Mach3 ceased nearly nine years ago. Notwithstanding that it still works and has a loyal fanbase it is obsolete.
Mach4 is current and still growing. I've been using Mach4 and an Ethernet SmoothStepper for 8.5 years, and its light years ahead of Mach3.