The mug warmer is nice/minimalist in design and works as described. My drink stays warm throughout the whole time it's on but the drink does get a bit hot if there is not enough liquid in the mug. The mug warmer did stain the circumference of my mugs a bit but I haven't encountered one that doesn't. I imagine it won't be a problem if you don't leave the warmer on for more than an hour at a time.