About the cumulative effect of 2.4GHz radiation, I'd say the jury is still out on that one
Thats definitely true. I'm not advocating a devil may care attitude, but there doesn't seem to be anything dangerous at all with regular normal use. Billions of people all over the world have been carrying out an experiment on themselves with HUGE amounts of cellphone usage over the last dozen years. A cellphone puts out a lot more power at your ear than the bt headphone does and at similar frequencies. And so far, with billions people, many of which spend hours and hours on these devices every day not a single study (decent, well done studies at least, plenty of alarmist stuff surfaces and then quickly goes away when people get a look at how they managed their data) of it has been able to find anything caused by it at all. When all this started I avoided cellphones for a few years to see what would happen, and nothing happened. I still dont spend hours and hours on my cell, but when my mom calls while i'm out I dont feel like it's hurting me to talk to her, at least due to the phone
Your BT headset puts out lots less energy than the cellphone does, and when it's not actually sending data it puts out very little at all. The power output is directly related to the amount of data they are sending out, just sitting there idle waiting for the phone to ring they only send a few bytes every so often to make sure the phone knows it's still there and such. So even if you wear it all day, you're only getting a tiny fraction of that energy transmitted unless you're actually on the phone. (this is why the standby time is so much longer than the talk time, both for phones and headsets)
So it's actually exposing your brain to less microwave energy to use a low power bt headset to talk to the higher power phone in your pocket. Course, that exposes your pocket to more radiation. Maybe better put the phone on the table in front of you...
While I would not be on the side of mandatory implantation of blue tooth devices, I just can't see any evidence of any harm that putting one in your ear for some phone conversations would do.