I agree completely and should have written this a long time ago. I bought mine originally for the 90 degree IEC connector to my S.E.X. amp and like you I was skeptical of any sound improvement. I will never go back to the stock power cord either. I heard more detail along with a more natural and relaxed presentation. I use my S.E.X. amp as a desktop speaker and headphone system so maybe the cable is able to reject computer and high frequency electrical noise. I can't explain it scientifically, I just know it works.
I recommend everyone build one of these power chords. Maybe you will hear an improvement too, especially if your amp is in an electrically noisy environment. Worst case is you will have a really nice power cord that sounds as good as any other but looks nicer on a Bottlehead amp.
Ken