Which criminals? The ones a local policeman happens to stop in a routine checkpoint?

I'd like to see actual stats on what percentage of everyday criminals who are met by local law enforcement "conceal billions of dollars".

I'd bet this percentage is so small the tool does more harm to the general populace than good on the off chance such a criminal is caught.

Yes, US citizens are criminals by definition of law, apparently.

  Many times, criminals illegally clone valid payment cards
  on to non-descript pieces of plastic like hotel room keys 
  and subway cards, making detection and interrogation 
  nearly impossible. Since virtually any plastic card with 
  a magnetic stripe can re-purposed as a credit, debit or 
  prepaid payment card, being able to determine the 
  identity of the card is critical to your investigation.

"The ERAD platform will help you document every confiscated credit, debit and prepaid card, and instantaneously provide key card issuer information that’s critical to your investigation. And if some of those cards are prepaid cards, ERAD™ gives you the ability, right at the point of arrest, to determine the value and immediately secure or freeze those funds."

So these devices do let LEOs seize funds but only from prepaid cards, apparently, for now.

http://www.nytimes.com/2013/10/17/us/justices-weigh-freezing...