The free TV Key is nothing really special and is basically just an antenna that picks up on all the local broadcast channels such as CBS, NBC, FOX, and PBS.
You do not get cable channels or other channels with the Free TV key that you cannot get over the air with your current TV antenna.
If you already have an antenna to pick up local channels for free then getting a Free TV key will do nothing to improve your channels.
You also need to be very near the TV station transmitter to pick up channels with the Free TV Key as it's a small antenna.
I had a free TV key when I was in an apartment in the city and it was okay and worth it but now that I live further away from the TV transmitter I had to have an outdoor antenna installed.