It is said that adding jewels on certain (metal-to-metal) points will reduce the total friction, which otherwise (with dirt and tear) will overcome the power of the driving train. Sounds promising and many report good results, but I don't think there are any actual empirical evidences / "proof" yet. If you like the rep, try it! Due to the high variation in build quality, some of these reps work well after a year while many others end up dead within a month (just from what I understood here on the forum).