[apecat]

The tradeoff seems to be that

* Bluetooth offers limited range and uses more battery, and is usually interrupted if someone calls, but supports any application that can play sound.

* Spotify Connect is its own Spotify client and downloads the audio stream from Spotify which allows freedom to roam. But the implementation is indeed limited to Spotify and doesn't support niceties like volume normalization or nerdy details like crossfade (and perhaps not gapless playback)