I covered your 'invalidation' already when I said 'for it to have any educational value'.
Problem #1 - 'un-networked' boxes are a fallacy. Everything is connected these days. Just ask the centrifuge guys in Iran. The 'air wall' effectively just does not exist. So if you're educating them under such a false perspective, what exactly is the value of what they're learning?
Problem #2 - hackboxes aren't targets. This would be like pinning rifles to the wall for target practice. It is again so very far removed from reality as to greatly diminish the value of what you're trying to teach.
Not everything has to be worth doing and useful to others. I get that. But these are education dollars we're discussing here, which are typically limited.