I don't own one, but I tried one with the bands at Sports Authority, and I didn't like it. First off, the bands don't give the kind of smooth resistance that a more professional machine does. (Maybe I've been spoiled by the nice machine at the gym.) For part of the motion, the bands help, then when you get to a certain point, they stop helping and you're on your own, lifting all of your body weight with no assistance. Hope that makes sense; it's hard to explain.
The other thing I didn't like was the way the platform you put your knees on worked. It tilts up and down, like a see-saw, rather than moving up and down staying parallel to the ground (hope I'm explaining that right). This means that at a certain point in the movement, the platform is tilted way down, and I felt like I was going to slide off, and it bothered my knees to kneel at that angle. The machine at the gym has a platform that moves up and down and doesn't tilt, and I like that much better. Unfortunately, all of the machines that I have seen in the $450-500 price range (even if they use weights instead of bands) have this tilting platform, so I don't think I'll be buying a home machine.
But everyone is different, and what bugs me (and my DH) might not bug you. Maybe you could try one at a store to help you make your decision. DH and I were ready to buy one until we both decided we didn't like the one we tried.