@Mm7,
There is a misunderstanding on that, the discount is on registration, not on delivery. The advert is quite clear. Marshalls have always been good with discounts 3 years ago, they had a zero AP on BMW. I think they go for the brand bonus during the low sales in the summer.
You need to make an appointment with the motobility guy, and finalise your deal. Test drives in a i35 are like hens teeth, so be prepared to take a drive elsewhere, ( in a m sport) as a private customer, if thats important to you.
You only have to visit twice, one to order, one to collect. Your local bmw dealer will deal with any faults, servicing ect.