Hello! I recently purchased the Bender Ball and a few workouts, from a local supplier here. For those of you thinking of purchasing online, my supplier (I'm in Canada) suggested a better website for US clients:
http://www.savvierfitness.com/
It's Bender Ball Pro, and you won't get all the billing problems of the other website. A friend of mine ordered from them and had no problems (and you can add a few gliders to your order, too.

Loooove my gliders!

).
I really, really like using the BB *for core*. I'm a convert. The core workout that came with my ball is about intermediate in level. The Advanced Core workout is tougher, and when I'm done all 15mins, I have a thorough toast in my whole core, but without conjoining fatigue in my hip flexors and lower back. Leslie comes from a pilates background, and the BB is just the pilates mini-ball, with her name stamped on them. The core work is primarily about working the transverse abs. Yes, of course all the rest of the core muscles get used, too, but because you're doing it all with your TAs contracted, you're developing great stabilizers, which are the most critical core muscles to strengthen IMO. Posture, posture, posture!!
Having given all the positive plugs, here's my negative comments: I think the best use of the BB is for core work, as well as butt/hips/thighs (floorwork type stuff). But to take it as far as she tries to with total body workouts, you're better off doing your other workouts. It seems whenever someone comes out with a new tool they want to claim it "does IT ALL"....and can even cook a 20lb turkey! I'm not impressed with the workouts that don't focus solely on core or hips/glutes. I did the Strong & Healthy Back workout once, and it left me with a really nice, stretched out back; sort of the same way yoga does. You do a gentle superman-type exercise that truly leaves you about an inch longer by time you're done. It's very nice. I think that workout will develop back flexibility, endurance, spinal stability, but isn't going to replace barbell rows or pull ups for lat development, etc. It's a great one for posture, but not muscle building.
Overall, I like to use the Advanced Core workout once a week (Cathe or my own core workouts other days), and the Glutes/Hips/Thighs workout once a week (as a "floorwork" session), and a Cathe floorwork session once a week. So, like anything, I don't put stake in any particular workout or piece of equipment being the Magic Bullet for the perfect core. The BB just offers another way of changing it up, keeping it fresh, and introducing something new.
The core workouts are 15mins long, the Back workout is 30mins, the Booty Bootcamp workout is just over 30 mins, and the Glutes/Hips/Thighs is 20mins. I think $20 is a lot to pay for one 15min workout, but also think the Advanced Core was worth it, given how often I use it. And while I won't use the other workouts regularly, myself, I will use them for ideas for working with clients.
HTH,
Sandra