When I spoke to Stuart E from Krazy Horse at RFTH 2016 he suggested that these are not necessary unless you go even further with tuning and start to look at the 128cu.in barrels etc. This was reiterated by their tech Dan when visiting their dyno last autumn. I don't doubt feedback that suggests smoother running, but they are probably not cheap and I'm not sure I want to go further on my car.....
Having said that, I am easily swayed if any more of you report smoother high-rev running and other tangible benefits!
