Works OK in my 2013 Dodge Challenger with 430n head unit. Calls work no prob, but occasionally I get 100-200ms breaks in audio when listening to music, be it locally stored or streamed from Spotify. Only happens once every few songs so I don't really care for right now. It doesn't happen with any of my Android phones or with my old 5s so I know it's related to the 6.
I ran in to a problem with the phone and BT in my car over the weekend. It seemed to have been working fine previously. Yesterday, it would send or receive calls. It kept saying switched to handset and when I would select switched to handsfree I would get an error. I went in to devices on the car Bluetooth menu and deleted all old phones (my iPhone 5s and my iPhone 6 Plus along with my wife's 5s). I then went in to iCloud and deleted my iPhone 5s backup from my cloud account. I then re-paired my 6 Plus and it is now working completely normal....strange. I guess that since I had restored the iPhone 5s backup to setup my 6 Plus that there may have been some confusion. Deleting everything and starting over fixed the issues. I'll try to experiment more today to see if it is really resolved and if everything is again working as normal.