Outputs the screen of the phone to the TV accurately, including reflecting whether you have it in landscape or portrait.
In applications that support it, only the video is sent to the TV - the on-screen control bar containing play, pause, rewind, fast forward and other notifications like the title of the video file only display on the phone screen, not on the TV, so that you can use the phone as the remote control without interrupting your viewing.
I'm using it with the Samsung Galaxy Note (I don't yet have a Galaxy S II to try it with). In fact the packaging doesn't mention any models specifically, just "Use only with compatible Samsung mobile devices. Refer to your device user manual"