What is that device that Finch gets out and puts on the desk on a few occasions when he's talking to Dominic?
Is it his own personal recorder or is it some kind of jamming device to prevent the conversation being recorded by state surveillance technology?
I took it as a jamming device.
Hitler! C'mon, I'll buy you a glass of lemonade.
I think you're right, I've just remembered the scene when V posing as Rookwood meets Finch and Dominic at the St Mary's memorial. The first thing V does is get out a device of his own, to which Finch says "We're not wired."
So yes, it looks like it was something used to prevent recording or surveillance equipment doing their jobs.
Yep, that basically confirms what it does.
Hitler! C'mon, I'll buy you a glass of lemonade.