Does the Proform Ab Glider work? What about the Ab Circle?

I bought the Ab Glider so I can speak for that. Terrible. Hurts the back and does not isolate on the straight-on crunch move. The crunch move your supposed to do to the sides is virtually impossible. I had several friends try it and no way - the video makes it look easy. Don't buy it. Then, the Ab Circle-like side to side move is sort of fun, but at the extreme left and right position, it is higher up dur to the design, so when you head back the other way, you start out downhill, so there is too much momentum - too easy...not enough "work". I got it for the Ab Coaster-like crunch but it is extremely disappointing. My health club has an Ab Coaster and I love it. Should've gotten that one; went cheap and learned a lesson.