What to look for in bone conduction headphones for bike voice navigation? I am getting lost. Easily. And looking too hard at the screen (phone mounted on the handlebars) makes me lose concentration. Luckily, Komoot I'm trying now, and Google Maps, provide voice navigation. The problem is, either I put it on speaker and I do not hear it on busy roads I need it the most, or I put it on the headphones and I don't hear other road users. Quite awful and safety issue either way.
I think that bone conduction headphones would solve that for me. But I don't know how to choose. Note, I am not looking for particular product recommendations. What's available for you now may be unavailable for me here and for sure will not be an optimal choice in two years. So I want to ask how to look at them? What really matters?.
What I need them for, in order of priority:

Hearing outside world.
Navigation, of course!
Listening to unobtrusive music. Quality does not need to be good, but no irritating squeaks and creaks.
Answering urgent phone calls.*

My rides are usually no more than 6 hours long with up to 4 hours of actual riding in it. Headphones needs to last that much. Ability to recharge from powerbank would be appreciated.
With this in mind, how should I proceed with selecting model for me?

* I'd prefer microphone that would work, but knowing there is a call would be enough - if there would be an unobtrusive way to reject that call or automatically stop ringing sound after one or two rings.
Point 1, hearing the outside world, is mostly easy.  If the audio is too-high a volume it can still drown out the background, but that's got to be quite loud.
Point 2, these headphones have to work with your device.  If that means bluetooth, then battery life becomes a consideration.  If your device has audio-output jack then that's another option. 
Do note - Bone conduction headphones use their internal battery all the time.  Bluetooth is additional power usage.
Generally speaking, the music fidelity of bone conduction head phones is down there with cheap AM radios.  So your point #3 is going to be hard to match.  It is certainly audible, but quality is low.   They are great for audiobooks though.
4, phone calls.  I have BC headphones that are just headphones, no microphone.  So they can beep should a call or message arrive, but I can't take the call.  There are variants that have a microphone and call control button.  If you use an audio out jack, you might need a 2.5mm 4 way TRS connector, or maybe a 3.5mm version.
Unmentioned - sweat.  Some BC headphones have a control box partway down the cable.  For me, that used to clip to the collar or the HRM strap, which worked well.  But sweat tends to get inside the controls and make them flaky, then non-functional.
Another feature, is some way to easily turn them off.  Ideally a button that you can hit without looking, that shuts off the sound should you need to focus on something else going on.
Cost is the last mention - you could spend multiple hundreds of dollars, but thats overkill for on a bike.  Something down around $50 USDish would be less upsetting when they do eventually break.