If you will always make a point to make an outbound call, "Auto Call Recorder" free will record both a bluetooth headset and the incoming caller's voice.
If though, you received the call, and then activate the BT, it will not record the caller's voice.
So, when I get a call I want to have both sides of it recorded, I just tell them, "I have to call you right back", and do it.
* Call Recorder - Auto Call Recorder Free - Android Apps on Google Play
I tried a lot of call recorders before I found this one, and it is the only one that has worked for me every time.
It just has that one little nuance that is probably a fault of Samsung's handling of the audio circuits.
I use it on a Samsung S5 and a Note 4.