Using 16.04/rc installed yesterday on Nexus 5, no major Bluetooth problems for me. Sometimes takes a couple tries to connect but seems to use high fidelity profile by default and switches output as soon as connected. Music player works really well with my 20+ GB MP3 collection too. Shows album covers from folder.jpg rather than demanding every song have the same image embeded, for example.

UBports really breathed new life into this old phone. Looking forward to the official release!