I hear that they are good. How much is the Project Zen versions going for?
I myself am running the older version of the STS RS3 engine. Had to change the conrod to a Nova one. More reliable. Overall bang for the buck I must say. But I hear the newer D3 and D5 ones still need their conrods to be checked once in a while.
I guess they are the same with Sirio engines. You need to check the conrod from time to time.