we have the mix stick's. Cassidy has gone through 3 of them...1 of her own doing but the others have just completely konked out on her. She bought herself a Sony MP3/video player for about the same price at the max and I have to say that's probably a better option for you/her for the trip.
Katie's got a mix stick, and likes it for her music. I'm looking for something that she can play videos on. Airplanes don't usually play movies that she would be interested in. I may have to break down and buy an inexpensive personal dvd player.