For testing something like that I would write two separate programs. I would get one of them to send "" once per second and I would use the 3rd example from Serial Input Basics on the other Arduino.
I can't think of any reason why it would make any difference using Nanos or Unos.
I have had another look at the datasheet. That seems to be a 3.3v device so you are likely to damage it by connecting it directly to a 5v Arduino.
...R