are they worth it and where could i get 1 from ?
Link to buy is at the end.
Read the link at the start and decide if it's worth it for you.
They are not hamonically damped like the original, I'd put it nowhere near any of my engines.
Unless you have your rotating assembly balanced they have the potential to damage your engine.
Having said that I put 10,000 miles with one on my K8 engine, with no apparent consequence. I don't have one on my ZE though, because I value the engine more.