Well, I can't tell you exactly how it will be... But if you bought the video from iTunes, the quality will probably be a lot worse than on the iPod. It takes a lot less pixels to make the quality of a video on the iPod good than on a TV, therefore when spreading the pixels out, the video will just look sketchy, and not as crisp. Overall, the quality is going to decrease.
I think it's worth it--to output video podcasts, photo slideshows, stored movie files to your TV from the iPod is quite cool. Of course, the quality will depend on the quality of the file you begin with, but I've found that done right, a video podcast is almost indistinguishable from broadcast TV show.
In the end, "worth it" is a subjective decision. It's not unsightly horrible, if that's what you're wondering. And remember, if you have a camcorder AV cable laying around, you can use it as well--just switch the red and yellow connectors when you plug them into your TV.
Yeah... I apologize if I my previous post gave the impression that an output cable for the iPod would be a waste of money. I was just trying to get the point across that most likely, the quality of the video will decrease on the TV, in comparison to the iPod. All in all, the cable will do what it's meant to do.