Thanks for the replies

I do absolutely NOT want a convex mirror (the zefal spy is, and the german mirror looks like it is, thanks for the suggestions anyhow)... I've tried them, and tried to get used to them, but cannot judge speed and distance accurately... vehicles seem first a long way away and slow moving then all of a sudden they're bearing down on you at seemingly galactic speeds :/ ymmv...

The Blackburn Helmet mirror seems to be flat (?? anyone know)... I'll have to give it a try...