I have the dvds that came with the tower, and like Barb I use them on the old tower. I also used the new tower at the Road Trip, but I didn't think the bar moved any more easily than the one I have, so I'm keeping my old tower. (Barb, here's a tip: I lubricated the sides with some silicone spray and now the bar moves MUCH more easily. It did make the sides kinda sticky though, so when moving the tower around I just hold it using workout towels so I don't get my hands slimy.)
The dvds are much easier than the typical Cathe workout, and much easier than the Fit Tower Advanced DVDs. Like Sherry said, they are good for a day when you're just not feeling it, or if you're recovering from illness or injury. I've also done two in a row. Another way to use them that I like is to do all of the legs from each disc, or all of the core. It's a pain to have to switch discs (I wish they were in the workout blender), but doing all of the leg exercises in a row (sometimes modifying to make the exercises more difficult) does get a bit of a burn going.
HTH!