If they work like the toning tables, then it isn't the same thing as exercise, since your muscles aren't really doing the work. You won't get much of a workout, if any at all. The machines are great for people that have certain health concerns and need to increase flexibility. They've even been shown to help lose a tiny amount of water weight (which will come back quickly) But they aren't going to help you burn fat or build muscle, which is the main point of exercise.
How I wish they did work, though, I'd probably have one in my living room
If you do decide to join, please try to do it short term and not sign a long term contract, just so you can be sure it's something your body will benefit from.