If it helps to have additional comments, then I agree that the new way of handling the temperatures is just awful. The underlying problem is that the firmware just sets the temperature; there is no "on" and "off". The heater gets turned off by setting it below room temperature. So if you add "on" and "off" buttons, you have to have some way not to confuse them with the temperature setting.
I do like the idea that the last set temperature gets read off the machine and plugged back into the software. That keeps the software in sync with the hardware. I also acknowledge that there are no perfect solutions for this problem. However, I would suggest that a reasonable solution is that whenever the controller board reports back that a temperature is set to zero, then the software should set the "off" button, NOT change the temperature value. If the temperature has been adjusted, say for a different type of plastic, then yes, the temperature value should be changed and the extruder should remain "on".