Cobblers. There is a major difference between operational security and capability. The former should legitimately be kept secret during a case. The latter should be fully disclosed, they work for society not the other way around.
This is just a way of generating fear and uncertainty in the populous in general - not just the criminal fraternity, and is just a variant of security through obscurity anyway.
Are these devices even legal anyway? Do they have a spectrum license or exception? I suspect the whole reason its kept secret is that these devices are operating in a very grey area of the law.
The cops need to be seen as totally compliant with the law - not seeking to exploit it. Especially since in most cases these are being used to catch your garden variety criminals.