Hi Apphugs,
First. i like your tool I'm still struggling with the functionality. Beside that I have some GUI wishes :-)
I'm not a fan of lots of open windows and OK buttons. To do this I would ask to merge all existing (4) windows of Modbus RTU Master into one window. That would help my self-organization :-)
Personally I see no need for OK Buttons in Modbus RTU Master. I would remove them. Changes can always take effect immediately.
Markus