Pretty good if you have the time to wait...

We got one of these before we went on a week-long church trip with our son when he was a baby. It did come in handy for having a place to store the bottles overnight without having to leave our room, but it did take a little longer than we would have liked to warm them at night.
I did like the fact that it was all self-contained. The little containers to store the small amounts of water needed to warm a bottle were neat and made it easy to use. But, you had to have an external source to freeze the insert for the cooler to keep the bottles in and it needed to be refreezed every day.
But, it did come in handy at night to keep us from wandering around in the dark or waking everyone up by cutting on every light in the house we were staying in during our trip.
Basically, if you have the time to wait, get it. But, sometimes it was easier to heat the bottle to room temperature just by holding it under warm running water at the sink.