The Introductory Kit is very similar to the type of pull-out that appeared in Dragon magazine when a new game was being launched, although this provides a lot more in terms of rules. If you are trying to entice your players into a game of Dreaming then this would be a good starting point.
The Kit walks you thorough all of the basic Kiths, Seemings and Courts found in the main rulebook, and covers Arts and Realms (Changeling magic). The rest of the Kit gives an overview of the game setting, the raison d'etre for Changelings and a basic guide to their society. There is enough information here for any group to make an informed decision as to whether they want to invest in the game.
I cannot speak highly enough of the full version of the game - it endures as my favourite World of Darkness game (Old or New) and offers such a rich a diverse opportunity for storytelling that you simply cannot run out of ideas. It is easy to run as a stand-alone, without encountering the other denizens of the World of Darkness, or even engaging in the evolving metaplot through the supplements.
My advice - pick this up (and encourage your gaming group to do so) and then buy the main rulebook. you'll not regret it.