1) You sure that's the best price? Looks like a buck cheaper on Amazon plus no tax and 7 bucks shipping. In other words--don't rush. Amazon is always cheaper than everyone.
2) If it was me personally, I wouldn't even consider it. But that's me. I'll tell you this, if it's just a fad that you'll use once or twice, then why bother? If you're both seriously going to use it to the point of wearing it out, hey, a little something is better than nothing, I guess.
3) A heavy bag and boxing gloves are cheaper. You'll, "tone and get some cardio," and you'll get fit and put on some muscle if you put in a bit more effort. Matter of fact, I can come up with a gazillion little work outs that will help you to, "tone and get some cardio," if that's all you're looking for, will you pay me the $600 for the info? God, the things I can do with a jump rope...