I'm happy with the audio performance of the adaptor (so I agree with most reviews here), but feel I should point out that the adaptor supplied may not be exactly the same as the one in the photo, as was my case:
In the photo, the plastic casing has a slim-diameter neck immediately above the metal plug. I have trouble finding adaptors that fit though the small jack-hole in Apple's iPhone4 'Bumper' case, & thought this adaptor would get around the problem due to its smaller neck design.... Unfortunately, the adaptor supplied did NOT have the smaller-diameter neck as shown in the photo (it's clearly a different (albeit similar) right-angle adaptor from the one shown on Amazon), so it wouldn't fit through the hole in the iPhone case.
I have other uses for it so don't intend to return the item, but thought other Apple 'Bumper Case' iPhone4 owners should be aware before buying the adaptor thinking it'll fix their headphone-jack woes.