Wow, I've just seen the weirdest phone holder… Just imagine a pirate's eye patch, rotated so that the patch is over the ear instead of the eye, and that it actually holds a phone.
Why would someone get something like this instead of a Bluetooth single beats me. Aesthetics perhaps, but that can't possibly beat the discomfort difference.
Autonomy? I would assume you can use a Bluetooth dongle for 24h without any charging cycle needed, but I can be wrong…
Temperature? Once again I don't know, but it is possible that Bluetooth dongles overheat on your ear during hours-long calls…
Any other ideas?