Plausible deniability refers to Nitrokey Storage's hidden volumes. They can optionally be setup, but no need to, and without the appropriate password it can't be distinguished. Similiar to VeraCrypt's hidden volumes.
So how long do they interrogate you before deciding there's really no hidden volume? And even if you do reveal a hidden volume, how could they ever know it's the only one? It's pointless, even if they know about the technology.
It really much depends on the individual case. In a constitutional state it should make a difference if obviously an encrypted volume is used or if there is the possibility but no certainty of one, two, three or four hidden volumes.
