if you live in a flat and have wooden rather than solid floors, it makes a lot of noise. Even with your own property, the sound that travels sounds disconcertingly as if you are having an energetic hump. This might improve or damage your reputation as well as keeping ylou fit.
The little ferrules tend to come off the legs unexpectedly so they can dig into flooring.
When they are dying, the springs fly off dramatically one after the other.
Apart from this list, we've worn out two over the years, but I don't think they add much in terms of exercise - you might gain more by wrapping up and going for a walk.