My BMW warranty has been hassle free and covered everything so far which has gone wrong. Its saved me in excess of £2500 and thats for a 2.0 2006 model with 50k miles and full BMW Service history, so you never know when things will go wrong!!
Warranty Direct were more expensive compared to the BMW warranty (£900 vs £360) and didnt cover the roof.
I will probably stick with the BMW Warranty with of course the other bonus that you take the car to BMW to have repairs done rather than a back alley garage.