Review on Ingecafea Coffee Mug Warmer for Desk Use - Upgraded Version with 4 Temperature Settings, 4-Hour ☕ Auto Shut Off, Waterproof Design - Ideal Gift for Christmas. Keep Your Coffee, Milk, and Tea Hot! by Lynn Cole

I'm convinced these new cup warmers won't get as hot as they did in the 80's or 90's. I used to have a Salton brand heater (which has died) but it kept my coffee very hot. This new one, with just an inch of coffee at the bottom of the cup (pictured), was barely warm. Sounds like you MUST buy and use a special flat-bottomed mug. In view of this, I do not recommend this one.