I'll tell you what is NOT hot! I have Phonak Audeos paired over bluetooth with my iPhone. A few years prior, I used to have Oticon, also paired with my iPhone. With the Oticon, if I made a cellphone call, the iPhone would use the default iPhone microphone while the audio would stream to my hearing aids. It was good that way because in a noisy environment I could hold the iphone right up to my mouth and the other part…
We ended up with Phonaks rebranded as Sennheisers. The audio quality during calls may not be as clear as a separate mic (what i believe you refer to as oticon), but from a user experience its nice to not have to fish out your phone to answer a call or wonder why you can hear the other person but they cant hear you.
Note that my complaint here is specific to Android support.