I think the conclusion I have come to about this matter after reading all the different views on here is that this mains issue is very system dependent & also power supply dependant as I imagine all who say they have not experienced a positive effect from mains leads are not lying & the same goes for those who have a positive effect like myself, I am certainly not lying about the results I experienced & was lucky enough to experience a very positive result from what amounts to a £7 mains lead I made myself, I certainly wasn't to go & pay lot's of money for this, just try something simple to hear if my system would benefit from it. I suppose the lucky ones are the guys on here who have not heard a difference, it probably means they have nice clean power supplies or their systems do not react badly to dirty mains supplies, good I say, save money & enjoy your music.
It seems silly to me for one side to say they are right & the other to say they are, I think both camps maybe correct here, be very interesting to see a large list of those who have tried this with no improvement & those who have experienced an improvement as to where they live, their own personal setups etc.. I suppose if this theory is correct no testing is going to work under lab type conditions due to the fact that it may vary widely with different mains supplies & personal systems.
If you did decide to try a cable start cheap like did, £7 isn't going to break the bank & if you hear no improvement I'm sure someone on here would purchase it from you & try it for themselves.