Not sure this hits your Qs exactly. But here goes what I do know...

I've got a Vantage M (the cheaper Vantage that has no barometer).

As I understand my watch it does not 'cast' its data real time - eg you can't have your Polar Vantage watch's wrist based optical HR be displayed onto a device on the bike hadlebars.

The Vantage is also bluetooth only. No Ant+.

My setup for HR is I still use a chest strap mostly - I have a Wahoo TickR chest strap and that outputs both Ant+ and bluetooth.
The Ant+ is used to display HR onto my Garmin Edge when on the bike.
And the bluetooth connects to the Vantage watch so I get more accurate HR on the watch (and on the run as well as bike obvs) than the optical HR will ever give. Doing that also automatically turns off the optical HR on the watch and so extends the battery even further (I was out for 14.5 hrs on my last event and the watch was still at 50% battery afterwards and had got back to my accom).

The polar units will not talk to each other. I used to have all polar set up but now just a vantage with chest strap and wahoo bike computer. The following may work for your set up though:

For races I set up my watch so it only reads out HR and speed during the bike leg in triathlon mode;

• don't pair your power meter to the watch (only the bike computer) and
• make sure your settings on the watch allow to share the HR data with other devices.
• This only works if you have a H10 polar chest strap setup (better data anyway) paired to both the watch and bike computer, the vantage wont share wrist based HR.

Then I just use my bike computer to give me my readouts during the ride as any other.

Hope this helps

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Matt Leu, M.S. Kinesiology
San Pedro Fit Works, Los Angeles, CA
Endurance Athlete and Coach
Consistency/time=results