The biggest problem is that a group that is supposed to work by rhythm is only as fast as its slowest members. So even if the greasiest deathfat in the room is at their limit struggling to keep up, the ordinary people there aren't even breaking a sweat. I have no idea how good a work out what they're doing is when done properly, I'm fairly sure a legit step aerobics class would look almost as stupid done by 300 lb lardballs.