I told her that, since I haven't actually tried any of those new abdominal machines yet -- and had very little knowledge about the Ab Circle Pro, much less the other two -- I couldn't provide an honest answer. The handful of reviews I've seen and heard for the Ab Circle seem to paint a similar picture: it provides a decent abdominal workout and a good low-intensity cardio workout, but it costs a lot, leaves you with "knee burns", and is easy to get bored with.
Personally, the boredom part seems obvious to me. While it's true that some machines make exercise more fun, the vast majority of them simply make you do the same boring movement over and over again like a hamster on a wheel. That's one of the main reasons why I avoid most exercise/fitness machines and focus instead on different types of "free-form" exercise (like bodyweight movements and free weight exercises). That being said, I really don't know how the Ab Circle Pro and its repetitive movements feel to someone using the thing on a regular basis. Shoot, maybe it really is like a "treadmill for the abs" and feels great when you're on the thing!
Here's what I do know: all ab machines, and 95% of fitness/exercise gadgets for that matter, are designed to leave you wanting more. What I mean by that is that, in reality, those thousands of late-night infomercial fitness and weight loss products aren't really designed to be super-effective. If any one of them was actually that great and helped the average person lose weight, get toned, build muscle, get six pack abs, etc. then people wouldn't need to buy anything else. Then the companies that make these products would stop making money and cease to exist. The goal is always to offer a relatively inexpensive, easy-to-use product that provides -- or at least has the potential to provide -- some sort of tangible fitness benefit, but is easy to get bored/frustrated with quickly and slide under the bed, out of site, so that it's easy to forget you never really used it and really wasted your money.... :-)
Anyway.... I felt bad that I wasn't able to help my friend with a real review or even a simple rating of the Ab Circle Pro. If you've used this "circle ab machine" and want to help us out, please leave your reviews, ratings, testimonials, comments, opinions, etc. in the area below. Thanks!