I would be extremely wary of any NON-Factory "extended warranty". From experience, the fine print will exclude just about every part that can go wrong. Mostly the extended warranties make money for the dealership.
Example would be most nationwide warranties will not cover things like the ECU, etc...
I would probably just suck it up, make sure you've got some cash handy for any needed repairs and move on.
'13 TiAg over Coral, 335is | DCT | Prem | L7 | Nav/Idrive | CA | 19" "-------"
A BMW is Just a Car, it doesn't make you smart, handsome, cool, or wealthy. Get over it.