This thing is a lifesaver! During my day I didn't have as many breaks to pump as I would have liked, so when I would get ready to head home, I would plug my pump into the lighter in my car and get all set up and pump on the way home. Since my commute was my time to decompress/relax and listen to music, I would actually get more milk then than any other time of the day, including first thing in the morning!
The car adapter works just as well as batteries or the wall plug. Definitely a great purchase even if you'll only use it a few times (long car trip, etc.).