LOVE the new Protoneer CNC shield and interested to see what effect the new input filters will have. The Pi version looks amazing for a PC free Cbeam machine but Mach3 for life! well maybe till mach4 is stable..... GRBL sure is rad but I find it hard to move away from Mach3 so decided to mod a v3.51 kits. I wanted better cooling to my drives and routed what would normally feed into an Uno out to a generic Mach3 BOB. I think next time I might move the stepper plugs to the under side of the board as well. So long as you don't forget the jumper setting are also "flipped" this mod has been super easy. Have a few worries about ground loops but going to hook things up and see if they are actually problems first. Fingers crossed it works rather than going up in a puff of smoke!