I honestly can't think of anything negative to say about the Ion Mug with charging coaster. I've been able to brew some tea and still enjoy it a nice & toasty 145 degrees 5 or 6 hours later! The outside of the mug warms slightly, but no where near at hot as a traditional coffee mug. I can use it both on and off the charger and it still keeps my teas toasty!  I definitely recommend it to all of my fellow tea and coffee drinkers! There's no need to keep running to and from the microwave warming a forgotten cup throughout the day!