I was looking for a USB mug warmer, but got this one by mistake.  I am SO glad I did!  Even though I had to use an outlet (which was in short supply), I love this warmer!  It heats up very well, keeps the heat right where it should be until I turn it off.  The only problem is that now that I've had it a year or two, the black where the mug sits is starting to wear off showing silver.  That makes me nervous.  So I am going to replace it - with another Mr. Coffee Mug Warmer!  Just wish I could find them in a store, not just online.