Does anybody have any expirience with these.

I saw some threats in the past for broken pulleys.

Is this the case? Can these things brake?

I am serously considering to put those on since there is a double benefit, less rotating mass and adjustability.

 

We have experience with these

See here https://www.scoobynet.com/group-buys...c-fitment.html

You won't gain much by the weight off them , it's adjusting the valve's is where you will get power gains from