I have got a light duty machine made in Devon (especially for cutting clotted cream ) unsupported rails make deflection a problem and engraving brass is a matter of trial and error, mainly error.
Engraving bits (V chisels) simply chew the brass for me and I think that may be a vibration issue due to poor rigidity. I get better results with a small end mill, typically down to 0.4 mm. I have tried 0.2mm but those buggers are so delicate, they will break if you even look at them funny. I have to use very low feed rates and DOC's and lots of WD40.

If I were doing it as a commercial venture, I certainly wouldn't use a Chinese low cost gantry machine. The second machine looks better, but again column rigidity could be an issue.