Sounds like the "or such" wins, but even with bluetooth speeds that means you're backing up 1-5 photos per minute and that helps a lot.

And harm a lot too, you phone can't deep sleep since it has to wake up periodically to process data from bluetooth stack. Combined with slow transfer speed, that gonna eat your battery like nothing.

Playing audio over bluetooth also wakes things periodically, but it uses almost no power. With a similarly competent design photo transfer should be very battery efficient.

No, most(if not all) bluetooth controller has audio offload, basically the cpu does not involve(or very little) when transfering data from storage to radio.

Don't you mean yes bluetooth controllers have audio offload? "similarly competent design" means you do the exact same thing in the other direction. Instead of rarely waking up the CPU to coordinate sending, you rarely wake it up to coordinate receiving.