Review on ANBANGLIN Auto Shut Off Coffee Warmer For Desk: Mug Warmer For Coffee, Tea, And Wax Cups, Heating Plate For Hot Beverages (Black - Mug Not Included) by Kim Conner

You definitely need a flat bottom mug. I've tried a flat, thick ceramic mug and a thin copper one it works ok. It isn't piping hot, even on the highest setting, but it is hot and stays hot.Pros:Does keep it hot - but barelyAuto shut offCons:My Blue is not really blue, more like midnight blue - almost blackReaching for the mug over the power button (right-handed) will sometimes turn the temp down unwittingly.