Hence why I said, used to, not, wanting a. I see no benefits to this engine over the equivalent petrol apart from MPG.
This would depend entirely on how you define an equivilent petrol. This is actually quite difficult in the current BMW range.
If the equivalent petrol is a 430i then there are considerable benefits - it is smoother, more refined, more powerful, offers a noticeable performance advantage is more efficient.
If the equivalent petrol is a 440i then there are no benefits apart from MPG - which is of course why this engine is barely offered in markets where fuel price is a triviality. But of course we don't live in those markets and our fuel price is not trivial therefore it's a fairly considerable benefit - but it's a financial decision.
The 430d is priced exactly midway between the 430i and the 440i. It's a couple of grand more expensive than a 430i and a couple of grand cheaper than a 440i.
Personally I don't think this engine works in a 4 Series convertible. It probably does in a 4 Series Coupe and it absolutely definitely does in a 5 Series or 7 Series saloon where the increased refinement is such that it works wonderfully with the car. It's not a sports car engine - which is why there is no Z4 SDrive30d.
I just think it's standard options (and even optional extras) are something I would expect to find in a BMW sales brochure 10 years ago. Having had a look at the options list of the old E82 1M, it's almost identical in kit levels and optional extras. I would expect the game to have moved on in 5 years and a whole new model.
Welcome to the law of diminishing returns. There is only so much you can really do and when your small coupe already has widescreen navigation, dual zone climate control, leather, Xenons, black panel display etc then enormous leaps in terms of offered equipment are not going to be found versus cars 5 years ago. Remember that generationally the generation the 2 Series is on began with the F01 7 Series 7 and a half years ago..
BMW's treatment of electric memory seats has always been bizarre - they went through a phase of including them as standard on the 'top' version of each model, so you ended up in odd situations whereby a Z4 3.0i and a 330Ci had electric memory seats as standard yet a more expensive 530i did not. They've sort of abandoned that premise now and the standard seats on some models are so electric that it's almost hard to justify the extra (On the LCI 5 Series the standard seat is fully electric with the exception of forward and backward, meaning its very hard to justify spending a grand for memory function!) yet on others leaving almost everything manual.