I got my husband an Ab Lounge for Valentine's Day (sweet, huh). Anyway, he used it a couple times before he quit working out again.
I haven't reallly done a workout on it, but I have tried it out. I got the cheapest version at Wal-Mart. The thing I don't like about this model is that you can't adjust it for varying heights. The part where your legs and feet rest is too long for me (I am 5'6").
Overall, I think you can probably get a good workout on the Ab Lounge, but I prefer to stick with Cathe for ab work. I have been tempted to use it in my rotation, maybe once a week. I just haven't done it yet.
If you have physical limitations that make it difficult to do crunches or ab work on the floor, this is a good alternative.
Hope this helps.
Tina