Quite powerful item with a utilitarian origin. I could see it existing, but with a more involved origin. Having a faultless forgery tool certainly falls in the wish-fulfilment magic item category akin to invisibility rings and flying items.
A solid 2.0 - OK idea but flawed. It certainly can be used, especially in the hands of a formidable enemy. Go to Comment
Its good - but perhaps not as world changing as some would think. A very, very big problem on all battlefields, but especially those of the middle ages and later, is communication. Having an omniscient general is only good if communications can support their directives, otherwise they will be able to do a great after-action report.
Better for intelligence gathering and like, where speed does not need to be tactical.
Combined with magic enhanced communications, we have an entirely different kettle of fish.