Bluetooth Speakers don't directly use the compressed format, but another format (in the worst case SBC) recompressed by the player. I've never seen one that supported MP3 compression.
Or did you mean native playback from sd cards/usb sticks?
Had my music on my phone as opus. Did not work on the bluetooth speaker of a woman i was involved it. Better sound at lower bitrate is worthless if you can't play it.
