This coffee warmer plate has been a real up and down purchase for me

The first time I used this, the black coating on the warmer plate started scratching off (I have been using a ceramic mug), and now it looks like my cat used it for a scratching post

How can you even consider this a coffee warmer when you cannot even get the warming plate to a high temperature when the darn thing stops warming every single time you take the cup off to take a sip

as well as with a flat-base, metal mug (as supplied in their deal option)