In general, I think you are right. I do some testing this way, now. But I'd like to be able to additional testing that exercises my whole application.

A perfect solution would be something that I could eventually use to create a small app that simulates one (or more) of our sensors that I could distribute to potential customers so they can try out our data logging client.

If I can use the same technique for testing as for the demonstration tool, that would be a big win. That way I can become intimately familiar with the emulated comm port and be certain that I won't hose anyone's system.