I've purchased many that were new in the clampack. In the past I've always opened the plastic but kept the cardboard insert.
If purchasing one now I might just keep it in the plastic, a way of showing that this knife has never been messed with by anyone.
One thing to be aware of, it may not be a permanent solution. The plastic turns yellow over time and becomes very brittle, making it difficult to maintain and awkward to store.
If you want an Old Timer for using, I would absolutely not buy a NIB example. These knives are now at least 15 years old and no more will be made ever. They are true collectibles in every sense of the word. If you want a user, you can buy lightly-used examples for cheap all day long.