I have a Plantronics Savi 740 that Lumia shows connected, however, it does not connect to incoming or outgoing calls.
It is intermittent which is even more frustrating.
I have not tested Bluetooth streaming from car audio system, I know I can stream with iPhone 6SPlus Spotify, will try 950 XL.
I have .29 update and Microsoft store swapped out unit once.
I still think Bluetooth, the daily or multiple daily reboots and battery are all software issues... think Microsoft needs a rockstar VP like Panos to take over the software side to have a rock solid OS.
I feel sorry for Microsoft in some way, I think they really want to sell their ecosystem to CIO's, including cloud, device and such, any smart CIO would throw MS rep out of the door if they showed off 950XL as finished product.
Vision is there..execution is lacking on Windows 10 Phone OS!!!