Syncing with Garnin connect has been available for a long time on RWGPS. It is a great feature and I am sure Garmin device owners love it.
I personally use Polar V650 and RWGPS.
Polar is not as big as Garmin but their products have a large user-base. Now that Polar has openly published the documentation on their API inviting developers to make use of it I think it would be beneficial for RWGPS to add the feature to connect with Polar Flow.
The API does not look overly complex and is well documented. RWGPS could allow to pull rides from Polar Flow and store them in RWGPS profile.