FWIW I bought mine cos they looked pretty and my bay has red bits, was a total rice purchase. Never occurred to clean existing ground points as it was purely a cosmetic thing, not an issue I was trying to solve. I can tell you they made an unexpected difference on my DE with 50k miles, not saying extra BHP obviously, but I find the revs drop off smoother on shift and idles more happily. I can sell believe that cleaning up earths would have done much the same. I certainly wouldn't have paid £90 for them as a purely cosmetic thing but I'm too lazy to knock up my own and £30 seemed not too offensive.