Aaron,
Because the kit can be ordered, I would interpret that he is not building more, and when the stock is gone, it will no longer be offered.
Any S meter can be fed to the A7 line displayed on the Nextion as the red bar.? You must adjust the voltage level to stay within the 0 to 5volt limit of the Nano.? Otherwise, you can damage the Nano.? The stand-alone Nano-based S meter adds more than just the S meter function.? It is integrated into the display(s), so the S meter value will be displayed.? More values become available with the second Nano addition.? You will need another 5volt source if you add the second Nano.? Note that I have not done this mod.
73
Evan
AC9TU