During creation I am asked to specify the MCU board I am using and the method of connection.
My real device is an Arduino Due with a Yun Shield.
Initially, I assumed that these choices would have a material effect on the behavior, but that does not seem to be the case. That is, the choices I make there (though not tested exhaustively) do not seem to effect either the app running the project or the environment of the MCU code.
I ended up specifying the Due as the hardware and basing the MCU code on the version for the Yun board.
This worked without issue (so far).
So the question is: Are these two questions just platform info for the Blynk developers, helping to, perhaps, set priorities or do they effect the MCU or app execution in a way I have failed to detect?
BTW, I am very impressed with the quality of the documentation, how easily it worked on the hardware and the breadth of coverage of user needs.