While I don't necessarily disagree with previous posts, I think the Autocar advice that the 125i SE is one to avoid is misleading when in their review they go on to extol the creamy engine, etc.
They should have made it clearer that in their view the Cabriolet is the one to avoid, not specifically the 125ti SE - I am sure the 120d or 123d cabrios are similarly compromised.
I think this just underlines the point generally that you either buy a cabrio for the image (so save some money and get a 118d) or a coupe for the driving experience, in which case the 135i would be fine.
Never could understand the M3 or previous-gen Z4M convertibles - probably most were autos or SMG anyway, so an auto 3.0-litre version would probably have suited most owners better.