'As long as a piece of string' springs to mind as there are so many variables.
The main problem will be the production of 'open' entities which will not be of much use in cnc.

When I worked for a local authority the package was used to scan developement plans so as to enter them into Autocad, and as such 'open' areas didnt have much meaning.
The main criteria was the quality of what you were scanning, the worse case I ever saw was when someone tried a fax and that what can only be described as NBG.
The other problem area is the original drawing line thickness as this will lead to problems in translation. From memory I think the package tries to overcome this by a process of 'line thinning', but you could end up with 'open' areas.
Try the free version, it will give you a taste for it.

Peter