I had Coverage one on my 530 touring. I hated dealing with them . Every time i tried to make a claim they had another reason why they would only pay for the gaskets and not the parts. A real pita.
As far as extended warrenties go I got a quote on my '08 and was shocked by the price that i got from the local BMW dealer. This was for a Secure Drive ( by Soverign General Insurance ) warranty . I then started to phone other dealerships ( Lexus, Toyota, Mercedes etc). They all offered me warranties.
The differences between them is about a couple of things; coverage and how they deal with you if you make a claim.
I selected a couple that I though would be good to deal with;
They are S.A. L. (by Industrial Alliance ) that i could get from the local Lexus dealer.
As well there was Lions Gate ( which also is the same as secure drive ) but cheaper that is carried by Go Auto here in Edmonton.
All of these insurance companies are listed on the web and you can get their local agent from there.
The other stipulation that i had was that i had to purchase my warrenty at least one month before my 4 yr warranty expired otherwise the price rose dramatically.
The price of the warranty varied depended on the coverage, milage that I wanted to cover and the time that the coverage was in effect.
I selected 5 more years and 100,000 km extra. The cost was $3,474 with a $300.00 deductable. ( from SAL). Granted I only have 21,000 km on my car now.