It's being kept such a secret because the government doesn't want you to know the police are running these devices for the NSA. I can bet you that they are getting copies of anything these things vacuum up.
That's the whole secret here the government has turned the powers of the NSA on the American people in the name of the war on drugs, and the war on crime by claiming they want to fight terrorism. People will give up freedom for that. They will fight tooth and nail the other two reasons. The NSA is providing information directly to local, state, and federal law enforcements on crimes committed by ordinary Americans.