It does what it needs to, albeit poorly, for a handful of cents per pen. Once you start viewing them as disposable instead of trying to keep them until they’re out of ink, it makes more sense.
These are the pens put out where they’re going to get lost or taken, pocketed by the general public. I’d say their biggest flaw is that they don’t work on hard surfaces, so they suck for signing receipts on counters.
With a few million people it doesn’t even need to be a specific bank. It would cause an enormous problem. Especially since we’re used to assets being digital these days. Request enough actual physical cash and it would rapidly reach a breaking point.