Retrobike is full of very sensible people.
Never heard about these bone conduction earphones, they seem very neat.
Originally I would ride wired earphones, with the wires going into the fanny pack I strap around my chest. I then finally decided to get wireless, which is also a bit safer as I did get tangled sometimes.
I use in ear, though not fully noise canceling. I can see all your points about road safety, and I do tend to pull out one of the phones when I'm on a very busy street, although if I am in an busy area I rarely am on the actual road because we have bicycle lanes. The bicycle lanes are shared with pedestrians, young teens on electric scooters and joggers.
As I ride a lot of gravel and fire roads I don't really bother too much about hearing stuff around me.
When I'm on the actual road, alongside the cars, it's usually on very barren stretches of country roads. I might sometimes lower the volume, but especially at night I'll spot the headlights behind me before I even hear them coming.