After much to-ing and fro-ing
scienceandtechnology finally admitted that they do not have any of the normal Jazz headphones left. If you order from them you will get a set of the iphone ones (new style with braided cables), although their listing still shows the non-iphone version.
I got a refund and a set of the iphone model by way of an apology.
Just as I was ordering a set of the original version from Amazon I decided to give the ones I had a go. I can't see anything wrong with the way they sound!
Having run an MP3 player through them for 12 hours or so I find them quite satisfactory. I can make out everything that is going on in the music I have tried (including the hiss on some less than perfectly digitised Pink Floyd) without any apparent distortion or blurring of the various instruments. They produce a similar volume level from portable MP3 players to the original earbuds.
They certainly look like alloy to me. They are obviously made in two parts, but there is no step between the black body and the silver front part.
The cable had set into kinks from the way it had been packaged, but I have been able to straighten most of these out fairly easily.
I'm hoping that the slider and shirt clip I have fitted will help sort out the microphonics from the cable.
Most interestingly I discovered that the microphone and button on these iphone headphones work perfectly well on my Android phone (Motorola Atrix running Gingerbread). I can use the button to bring up voice commands or to pause/play MP3s (Winamp), including when it is locked. Very useful since commuting is the main thing I wanted headphones for.
Thanks for putting me onto these headphones guys, hopefully some of the above will help anyone else looking for a set.