I have not had any experience with them, but I can say that with a conventional timing chain I have found them to be quiet, require minimal lubing, and rarely need adjustment for tension. So all you are left with is the weight saving and the novelty/bling factor. It would be interesting to know how efficient they were. They can't be exactly the same as a chain. It would only have to be a tiny bit less efficient to cancel out the weight advantage. On the other hand if it were slightly more efficient then that would be another advantage in their favour.