Product review (2 stars): Metal jacket around cartridge drastically reduces heating area. Also introduces air gap.
The problem with the black metal jacket around this thing is that when you place slightly larger skillets, the base extends beyond the glass and hence there is a airgap between the glass and the skillet and this is a total waste of heat. Next because of the metal being bent at one end (so one can easily lift the thing off, the area available to keep larger sized skillets is drasticallly reduced. This should not be purchased at all. The original cartridge without any metal jacket around is perfect.