General rule of thumb; most anything that Billy May's yells about, should be avoided. The ShamWow guy comes next.
Most fitness crap (it's just that) should be avoided if seen on TV. Larger malls have a As Seen On TV style store where you can check out a few of those exercises devices, if your lucky. Most of that stuff is low grade plastic, badly designed and not meant to last but a little bit longer than your third and final payment of $39.95. A majority of those company's are out side the U.S. and will run ads on mainland TV, magazines and papers. Many class actions against their products, by kind of hopeless in the long run. Buyer Beware.
A friend of mine downloaded (torrent) the whole P90X workout program. Pretty solid training program, though many different forms of these style workouts have been used for years. Good investment in training time and effort if stamina, strength and lean muscle mass is your goal. But than again, not meant for everyone's goals .Good luck.