I have a cheap@$$ BT speaker that was given to me, which I carry in the top mesh pocket of my trunk bag. It's awkwardly shaped with no other good way of mounting it anywhere. I have to turn it up to max volume to hear it, and even then sometimes I can't hear it with the wind noise.
On my 31 mile commute I pretty much never see a single cyclist anywhere else at all. So I really don't care who hears what I'm listening to. The motorists will be past me in a split second, and I will be past any pedestrians in a split second (also almost none of those).