Product review (5 stars): Exactly what I expected
I waited awhile to review this because I wanted to give an accurate accounting.  I have had no problems with the knobs slipping or cracking.  While out of plastic they've held up well.  I think the mistake some people make is they simply turn the knob to turn it on.  Because of the point of resistance you must push down on the knob to get beyond that point then turn it.  If you do not push down on it the knob will split over time.