i have it and have used it occasionally - Drawbacks are exactly what you said - smaller than a warming drawer, and you have to remove the warming food to use the microwave for other things. But it does keep the food warm, in a comparable way to a warming drawer, IMHO. How often would you use it? Is saving 1000K a big factor to you?
I did not have a warming drawer until recently when I did a mini reno of my kitchen and got a GE Profile slide-in induction range that comes with the warming drawer. Nice feature, but I lived without it for 30 years.