I have one black 21st Century iron, 3 of the Top Flite style not all of them have TF on them, and 2 trim irons. The TF style only have one plastic part the knob. The 21st Century seems to be the most stable on heat but I check them all with a coil thermometer often when covering. They were all bought used so age could be a factor. I hope you will give us a full report on how the Prolux iron works for you.