warming breast milk on the go?

Hello ladies, has anyone used this to warm their breast milk while they are on the go? I want to know if it works well, or even if you've never used it, do you hyave any tips on how to warm the milk other than hot water. I usually just run it under hot water at home, but sometimes you're somewhere that you dont have that option, and I'm trying to cut down on the amount of stuff i carry around, so i dont really want to carry around hot water and extra cups wherever i go, i have two kids, so i already carry a huge diaper bag. lol

it says you can plug it into the car, house outlet, portable battery pack and laptop..