First of all, you should pay attention to stiffness. Even the prettiest-looking engraving with moderate stiffness (e.g. twisted from aluminum profiles) will not ensure proper operation. It may, however, result in jagged edges, burrs, and a distinct vibration pattern of the tool during operation. The machine cannot have sliding elements because it will quickly precipitate and will be loose. So there must be linear rolling bearings and ball screw gears that will allow to eliminate backlash.
As for the control system, engravers communicating with a PC via a serial or parallel port are no longer a thing of the past. During large works, especially in 3D, a file can reach several dozen megabytes. Currently, only Ethernet and technologies based on it are at stake, which enables comfortable operation of the machine with full visualization during operation in real time.
The control software is also very important. Forget about the printer driver that can be “printed” to the engraving machine. The software controlling the engraving machine must generate the tool path by itself (internal and external correction, up-cut and down-cut machining, pocket selection, pocket selection with island detection, work on many stages of plunging, cutting corners with an engraving cutter, etc.
And the speed – the fastest ones reach the feed speed of up to 1500mm / s, but 150mm / s is enough, machines whose speed does not exceed 50mm / s are toys.