I like Newton's cradles. I like the opportunity they present to discuss conservation of energy. I also like the sheer mesmerizing effect of the balls clicking back and forth, and the different patterns you can make.
There is a tendency with these toys to be made very cheap and lightweight. Unfortunately this leads to more of the energy being transfered in ways that aren't so pleasing on the eye. In this case after 20-30 seconds the clicking stops and all the balls just swinging slightly. I've seen others that are worse, where the show last less time.
I wouldn't say this is a bad toy, and indeed out of the ones available at the time of purchase, it was probably the best I could find. It was pretty cheap, and therefore satisfactory. However if you're after a long-lasting effect, you're going to need to pay a lot more.