I don’t really think you’re ever better off buying a brand new car unless it’s a special circumstance…I’d rather let someone else pay for the first year of depreciation…
THE CPO Warranty is only an extension of the factory 4y/50K warranty…it is different.
http://www.bmwusa.com/CPO/Benefits/Warranty.htm
…but the 4yr/50K warranty is pretty generous…it covers just about everything including brake pads and rotors…