The risk would be during transmission and not during reception on the bluetooth device, right? So you could listen to music, but if you were speaking on the bluetooth mic, you'd be exposed.
Although, even several Wifi devices could superimpose up to a strong amount of radiation. There's no point testing safety of just one device at a time, when people are generally exposed to combined radiation from several at a time.
Microwave ovens are the worst though. Never be near one when it operates. There's a reason it trashes Wifi reception when it's on. Mobiles phones are the second worst (speaking of 4G band) due to the distance they need to cover. Wifi is the weakest of the three. But even that could be bad over time.
Put one beside your head, and you may even feel it. Here's a self-blind experiment: Have someone turn on or off the wifi device while it's touching your head (without you being able to tell), and try to predict if it's on or off. Do 20 trials. Compare your prediction against a coin toss (serves as a truly random control) to see if it's significantly better.