I run that exact setup and really like it. It lets me not have to worry about a computer connected to the Xcarve or an internet signal. You upload the gcode to cncjs and away you go. I love having my Pi camera watching the XC and the feed right in the screen.
There have been a couple of issues with the latest versions where the app disconnects while jogging or if it sits for a while that seem to be related to an upgrade of a dependency.
The forum through github has been terrific and the main contributor ( Cheton ) is great about taking feedback and quickly adding new features. He added a way to have a second camera after my request and I think it was a week later. There are a number of feature requests out there that will really make it nice I think.