Banks can count, inspect and certify 50 bennjamins in less than 10 seconds.
It ain’t rocket surgery.
Those pens only detect starch. Counterfeiters learned to use starch free paper a very long time ago.
The pens essentially only work if an idiot makes a counterfeit bill.
The pens don’t work at all with any serious counterfeiting operation.
Actually, some of the counterfeiters have a method to defeat those pens now.
I know this because my bank held a training session on counterfeit bills when the business community had a spate of them for a while.