I took out the Insured Warranty at £39 per month as I opted for the £100 excess.
I've just had both seatbelt pre-tensioners replaced under the warranty but BMW waived the excess as it was a recurring issue. Given that the cost of a major repair is huge I'm ok with it.
It's a monthly policy so I can stop it at any time.
Just a word of warning. My dealer stated that any warranty repair is only guaranteed to the end of the warranty period, so for instance, if my brand new clutch starts juddering again then it would only have had 1 months warranty cover under the original term. He says that BMW don't give any parts guarantee of stuff that has been fitted under warranty other than the remaining warranty period.
I'm not sure this is the case, perhaps some of you more knowledgeable guys could confirm if they have to provide a one or two year parts guarantee despite the warranty?