Some people may want to use the Dremel Rotary Tool with the flex arm, which is fine and dandy, but I prefer to use an etcher. In my opinion you have much greater control with the etcher. The Dremel Rotary Tool doesn't have the ability to do the extremely small details like the etcher does. An inexperienced, or experienced, hand will find the dremel loves to run away on it own, simply because of it's rotary nature.
Think of the Dremel Rotary as a Sharpie, and the etcher as a sharpened pencil. That'll give you an idea of how different the results will be.