With my Nexus 5 I'm able to play music on a JBL Clip 3 and also on my Beats Studio 3.
I don't remember if I tried to use the microphone or be in call on both these devices, I'll come back if I do :winking_face:
On OTA-14 btw

Hum strange.. For me I just have to quit and reopen the app after setting a DPI value to see a change.
I was not able to run geary or fbreader on my phone tho, but with Firefox I can scale with no problem

Hi! You might want to use Libertine Tweak Tool (available on the store). You'll be able to scale your apps by setting a DPI value (I'm using 220 on N5)