Have you tried HipHopAbs? I think the program is rather over priced but maybe it is worth it, if it works. It is a series of cd's which you use to tighten everything up. We Wish. I have a elliptical bike right now and it is great.
I watched the ad on TV last week. As far as tightening abs, I really don't know if it works, but it would be a good aerobic workout. Of course, you already probably do an aerobic workout on the bike, right? So I can see why you would be looking to work on the abs.
It would be fun to try, but I agree about the price. I don't want to pay that kind of money just to try something. I noticed quite a few listed on ebay, but the bidding is fierce. You might save a little that way though.
I really don't have an answer to your question. But I was thinking about it when I watched the other day.
Did you get the DVD's or decide not to?