I’m currently building my MPCNC with this setup… Uno and CNC Shield running grbl. I don’t plan on using the MPCNC for printing or running jobs from SD cards, so I think the Mega/Ramps setup is overkill for me.
I currently have everything moving. I’m getting limit switches setup and getting familiar with the CNC workflow. I hope to start cutting this weekend.
If you want any info on setting this up, take a look at the xcarve or shapeoko communities, as they primarily use an Uno running grbl.