I'm still in the early stage of getting a gRex 100 up and going. As with all things ethernet/RS232, unless you do networking and or serial communication work frequently, just establishing communication can be very frustrating. Once you get past this what seems an insurmountable hurdle, it usually seems trivial on the other side, when you get there.
However, I thought I had made it and now am having repeated trouble in establishing and keeping the ethernet connection via Mach3 plugin. It seems ify on the gRex loader as well when it starts misbehaving. I'm uncertain if it is gRex firmware and communication protocol, hardware and temperature, or the 1-hour unlicensed plugin difficulty. If it is the later, it seems to me that the 1-hour limit is really short when you are still in the setup/evaluation phase. I may have to further investigate the USB route and non-Mach communications to make a conclusion on if the decison to go with the gRex was a little premature. I think it has great potential, if it proves to be more reliable than the parallel port/BOB direct communication shortcomings.
I anxiously await other posts on their success and failures with the gRex. I'm still hoping that this will be the start of a long and happy relationship with some addtional gRex's to follow, if we don't go our separate ways.