The main difference between a router and a rotary engraving machine is the type and thickness of materials that can be used. This is largely due to its power. CNC routers can engrave and cut out thicker and harder materials as the spindle motors are typically more powerful than engraving machines. There is also more Z clearance on a router.
A larger build combined with more power allows the router unique capabilities that a rotary, or even a laser machine, doesn’t have. CNC routers have the ability to mark metals, including stainless steel, without the extra time and expense of applying a chemical coating. Typically, they can have several different types of heads mounted to them so that one machine can have the ability to use a routing spindle, engraving head, oscillating knife and camera registration system for cutting out printed substrates. They are cost efficient, inexpensive to maintain, and easy to use
When deciding between the two, also consider what kind of look you are going for. CNC routers form facets when cutting, creating depth and richness in the look of the finished product. When cutting materials out, routers can produce beveled edges, so they are not sharp on the sides.
—Melissa Williams, Vision Engraving & Routing Systems