Without any details on the quantum resistant methods, its a fair...

Without any details on the quantum resistant methods, its a fair bet SEN makes use of one time pads or similar as public/private key methods seem inherently vulnerable to quantum computing, as I understand both technologies (which is an interested generalist).
But for the applications they have, of point to point encryption where each end is controlled and trusted, that is fine.

As for whether quantum tech exists? Who knows. I can't see the US intelligence services releasing anything for general consumption until they have wrung all the internal value out of it - which means their adversaries have deployed effective countermeasures. But it seems like it is more likely to be refined by a nation state than a company or academic first, given the value to those players exceeds any number of dollars.