I just got one to claim the digital copy of the last Harry Potter movie that comes with the blu ray. I'm not really that fond of it. You have to sign up for two accounts on the two sites, then make sure they're linked together properly. Then you have to download Flixster's buggy software to download your movie. It was a huge process.
The only thing I like is you can stream your saved movies to the Flixster app on your phone.