I purchased this product because I can't stand my coffee getting cool. It does just what I wanted it to do. Fits all my different size coffee mugs. The reason I gave it 4 stars is because the other morning (around 14 times I've used it) I turned it on but the light didn't come on, it didn't get hot. I checked my plugs turned it off then back on and the light came on and it started to warm up. I'm hoping this was just a fluke and not a sign that it's going to stop working after just a couple of uses....