I think you need to look for a car where the chain has been done, unless the owner can prove it has been done, walk away.
Once the chain has been done, as long as you use the correct oil (it is 10w 60 in the early cars 2007-2008 period due to a different bearing fitted in the crankcase that required a higher viscosity oil with more protection) and keep it topped up you have no worries. Later engines take more regular 0w 30 BMW LL04 oil.
Most of the problems people will have had with the timing chains is in cars where the engine oil was not kept topped up properly with oil, so where the chain which was 'wet' (needed bathing in oil) ran over the plastic tensioner guides they wore or broke up and allowed the chain to run slack and timing go out.
It's true that the later cars after summer 2009 have a smaller differential case. Its surprising the number of differences between my Jan 2008 coupe and Oct 2010 coupe, even the oil filter cap is different (yes oil filter, not filler!) as I found out when I went to swap the one I'd araldited 'dimple' magnets to on to the new car, not only was the hex tool required different the thread was too!
I think they are very nice cars, just some jobs are awkward like the glow plugs, but that goes for many modern cars, if you are going to pay a good independent to service the car no worries, but if you like to tinker yourself brace your self for some fiddly jobs. If you find one thats full bmwsh more or less happy days, but I'd still then head for a knowledgable independent thereafter, otherwise its plenty of ££££s to keep that up.
My 2008 car has nearly 225,000 on the clock and the 2010 car 143,000. I wouldn't have bought the new one if I hadn't found the previous owner of mine had screwed the glow plugs up. If it wasnt for the fact it had a noisy diff too and needed paint I'd have stuck with it. If anybody fancies a nice project car with some dents to fix, a diff overhaul required and glow plugs to extract make me an offer lol!
