The only real problem with my M1 is that the temperatures seems to be 20C off. I get first crack at 180-185 Celsius instead of 200-205 Celsius. Not sure why if it is sensor placement or a calibration issue. I usually roast to 15-20 C after first crack so it doesn't really matter that much. I take a note of the first crack temperature and add to that to find out my target temperature.